38856 Federal Register /Vol. 62, No. 138, Friday, July 18 ... · 18.07.1997 · 38856 Federal...

38856 Federal Register / Vol. 62, No. 138, Friday, July 18, 1997 / Rules and Regulations

ENVIRONMENTAL PROTECTIONAGENCY

40 CFR Part 50

[ADA–95–58; FRL–5725–3]

RIN–2060–AE57

National Ambient Air QualityStandards for Ozone

AGENCY: Environmental ProtectionAgency (EPA).ACTION: Final rule.

SUMMARY: This document describesEPA’s decision to revise the nationalambient air quality standards (NAAQS)for ozone (O3) based on its review of theavailable scientific evidence linkingexposures to ambient O3 to adversehealth and welfare effects at levelsallowed by the current O3 standards.The current 1–hour primary standard isreplaced by an 8–hour standard at alevel of 0.08 parts per million (ppm)with a form based on the 3–year averageof the annual fourth-highest dailymaximum 8–hour average O3

concentrations measured at eachmonitor within an area. The newprimary standard will provide increasedprotection to the public, especiallychildren and other at-risk populations,against a wide range of O3-inducedhealth effects, including decreased lungfunction, primarily in children activeoutdoors; increased respiratorysymptoms, particularly in highlysensitive individuals; hospitaladmissions and emergency room visitsfor respiratory causes, among childrenand adults with pre-existing respiratorydisease such as asthma; inflammation ofthe lung, and possible long-term damageto the lungs. The current 1–hoursecondary standard is replaced by an 8–hour standard identical to the newprimary standard. The new secondarystandard will provide increasedprotection to the public welfare againstO3-induced effects on vegetation, suchas agricultural crop loss, damage toforests and ecosystems, and visiblefoliar injury to sensitive species.EFFECTIVE DATE: This rule is effectiveSeptember 16, 1997.ADDRESSES: A docket containinginformation relating to the EPA’s reviewof the O3 primary and secondarystandards (Docket No. A–95–58) isavailable for public inspection in theCentral Docket Section of the U.S.Environmental Protection Agency,South Conference Center, Room 4, 401M St., SW., Washington, DC. Thisdocket incorporates the docket from theprevious review of the O3 standards(Docket No. A–92–17) and the docket

established for the air quality criteriadocument (Docket No. ECAO–CD–92–0786). The docket may be inspectedbetween 8 a.m. and 3 p.m. on weekdays,and a reasonable fee may be charged forcopying. The information in the docketconstitutes the complete basis for thedecision announced in this final rule.For the availability of relatedinformation, see ‘‘SUPPLEMENTARYINFORMATION.’’FOR FURTHER INFORMATION CONTACT:David McKee, MD–15, Air QualityStandards and Strategies Division,Office of Air Quality Planning andStandards, U.S. EnvironmentalProtection Agency, Research TrianglePark, NC 27711; telephone: (919) 541–5288; e-mail:[email protected] INFORMATION:

Availability of Related InformationCertain documents are available from

the U.S. Department of Commerce,National Technical Information Service,5285 Port Royal Road, Springfield, VA22161. Available documents include:

(1) Air Quality Criteria for O3 andOther Photochemical Oxidants(‘‘Criteria Document’’) (three volumes,EPA/600/P–93–004aF through EPA/600/P–93–004cF, July 1996, NTIS # PB–96–185574, $169.50 paper copy, $58.00microfiche).

(2) The Review of the NationalAmbient Air Quality Standards for O3:Assessment of Scientific and TechnicalInformation (‘‘Staff Paper’’)(EPA–452/R–96–007, June 1996, NTIS # PB–96–203435, $67.00 paper copy and $21.50microfiche). (Add a $3.00 handlingcharge per order.)

A limited number of copies of otherdocuments generated in connectionwith this standard review, such asdocuments pertaining to humanexposure and health risk assessments,and vegetation exposure, risk, andbenefits analyses can be obtained from:U.S. Environmental Protection AgencyLibrary (MD–35), Research TrianglePark, NC 27711, telephone (919) 541–2777. These and other relateddocuments are also available forinspection and copying in the EPAdocket identified under ‘‘ADDRESSES’’.

Electronic AvailabilityThe Staff Paper and human exposure

and health risk assessment supportdocuments are now available on theAgency’s Office of Air Quality Planningand Standards (OAQPS) TechnologyTransfer Network (TTN) Bulletin BoardSystem (BBS) in the Clean Air ActAmendments area, under Title I, Policy/Guidance Documents. To access thebulletin board, a modem and

communications software are necessary.To dial up, set your communicationssoftware to 8 data bits, no parity andone stop bit. Dial (919) 541–5742 andfollow the on-screen instructions toregister for access. After registering,proceed to choice ‘‘<T> Gateway to TTNTechnical Areas’’, then choose ‘‘<E>CAAA BBS’’. From the main menu,choose ‘‘<1> Title I: Attain/Maint ofNAAQS’’, then ‘‘<P> Policy GuidanceDocuments.’’ To access these documentsthrough the World Wide Web, click on‘‘TTN BBSWeb’’, then proceed to theGateway to TTN Technical areas, asabove. If assistance is needed inaccessing the system, call the help deskat (919) 541–5384 in Research TrianglePark, NC.

Implementation Strategy for RevisedAir Quality Standards

On Wednesday, July 16, 1997,President Clinton signed amemorandum to the Administratorspecifying his goals for theimplementation of the O3 and PMstandards. Attached to the President’smemorandum is a strategy prepared byan interagency Administration groupoutlining the next steps that would benecessary for implementing thesestandards. The EPA will prepareguidance and proposed rules consistentwith the President’s memorandum.Copies of the Presidential document areavailable in paper copy by contactingthe U.S. Environmental ProtectionAgency Library at the address under‘‘Availability of Related Information’’and in electronic form as discussedabove in ‘‘Electronic Availability.’’

The following topics are discussed inthis preamble:I. Background

A. Legislative RequirementsB. Related Control RequirementsC. Review of Air Quality Criteria and

Standards for O3

D. Summary of Proposed Revisions to theO3 Standards

II. Rationale for the Primary O3 StandardA. IntroductionB. Elements of the Primary StandardC. Communication of Public Health

InformationIII. Rationale for the Secondary O3 Standard

A. IntroductionB. Need for Revision of Current Secondary

StandardC. Final Decision on the Secondary

StandardIV. Other Issues

A. Cost ConsiderationsB. Margin of SafetyC. Comment PeriodD. 1990 Act Amendments

V. Technical Changes to Part 50VI. Revisions to Appendices D, E, and HVII. Regulatory and Environmental Impact

Analyses

38857Federal Register / Vol. 62, No. 138, Friday, July 18, 1997 / Rules and Regulations

1 A more complete history of the O3 NAAQS ispresented in section II.B. of the Office of AirQuality Planning and Standards Staff Paper, Reviewof National Ambient Air Quality Standards for O3:Assessment of Scientific and Technical Information(U.S. EPA, 1996b).

2 The Staff Paper evaluates policy implications ofthe key studies and scientific information in theCriteria Document, identifies critical elements thatEPA staff believes should be considered, andpresents staff conclusions and recommendations ofsuggested options for the Administrator’sconsideration.

A. Executive Order 12866B. Regulatory Flexibility AnalysisC. Impact of Reporting RequirementsD. Unfunded Mandates Reform ActE. Environmental JusticeF. Submission to Congress and Comptroller

GeneralVIII. Response to Petition for Administrator

Browner’s RecusalIX. References

I. Background

A. Legislative RequirementsTwo sections of the Act govern the

establishment, review, and revision ofNAAQS. Section 108 (42 U.S.C. 7408)directs the Administrator to identifycertain pollutants which ‘‘mayreasonably be anticipated to endangerpublic health or welfare’’ and to issueair quality criteria for them. These airquality criteria are to ‘‘accurately reflectthe latest scientific knowledge useful inindicating the kind and extent of allidentifiable effects on public health orwelfare which may be expected from thepresence of [a] pollutant in the ambientair ***.’’

Section 109 (42 U.S.C. 7409) directsthe Administrator to propose andpromulgate ‘‘primary’’ and ‘‘secondary’’NAAQS for pollutants identified undersection 108. Section 109(b)(1) defines aprimary standard as one ‘‘the attainmentand maintenance of which in thejudgment of the Administrator, based on[the] criteria and allowing an adequatemargin of safety, are requisite to protectthe public health.’’ The margin of safetyrequirement was intended to addressuncertainties associated withinconclusive scientific and technicalinformation available at the time ofstandard setting, as well as to provide areasonable degree of protection againsthazards that research has not yetidentified. Both kinds of uncertaintiesare components of the risk associatedwith pollution at levels below those atwhich human health effects can be saidto occur with reasonable scientificcertainty. Thus, by selecting primarystandards that provide an adequatemargin of safety, the Administrator isseeking not only to prevent pollutionlevels that have been demonstrated to beharmful but also to prevent lowerpollutant levels that she finds may posean unacceptable risk of harm, even if therisk is not precisely identified as tonature or degree. The Act does notrequire the Administrator to establish aprimary NAAQS at a zero-risk level butrather at a level that reduces risksufficiently so as to protect publichealth with an adequate margin ofsafety. The selection of any particularapproach to providing an adequatemargin of safety is a policy choice left

specifically to the Administrator’sjudgment. Lead Industries Associationv. EPA. (647 F.2d 1130, 1161–62 (D.C.Cir. 1980)).

A secondary standard, as defined insection 109(b)(2), must ‘‘specify a levelof air quality the attainment andmaintenance of which in the judgmentof the Administrator, based on [the]criteria, [are] requisite to protect thepublic welfare from any known oranticipated adverse effects associatedwith the presence of [the] pollutant inthe ambient air.’’ Welfare effects asdefined in section 302(h) (42 U.S.C.7602(h)) include, but are not limited to,‘‘effects on soils, water, crops,vegetation, manmade materials,animals, wildlife, weather, visibility,and climate, damage to anddeterioration of property, and hazards totransportation, as well as effects oneconomic values and on personalcomfort and well-being.’’

Section 109(d)(1) of the Act requiresperiodic review and, if appropriate,revision of existing air quality criteriaand NAAQS. Section 109(d)(2) requiresappointment of an independentscientific review committee to reviewcriteria and standards and recommendnew standards or revisions of existingcriteria and standards, as appropriate.The committee established undersection 109(d)(2) is known as the CleanAir Scientific Advisory Committee(CASAC), a standing committee ofEPA’s Science Advisory Board.

B. Related Control Requirements

States are primarily responsible forensuring attainment and maintenance ofambient air quality standards once EPAhas established them. Under section 110of the Act (42 U.S.C. 7410) and relatedprovisions, States are to submit, for EPAapproval, State implementation plans(SIP’s) that provide for the attainmentand maintenance of such standardsthrough control programs directed tosources of the pollutants involved. TheStates, in conjunction with EPA, alsoadminister the prevention of significantdeterioration programs (42 U.S.C. 7470–7479) for these pollutants. In addition,Federal programs provide fornationwide reductions in emissions ofthese and other air pollutants underTitle II of the Act (42 U.S.C. 7521–7574),which involves controls for automobile,truck, bus, motorcycle, nonroad engine,and aircraft emissions; the new sourceperformance standards under section111 (42 U.S.C. 7411); and the nationalemission standards for hazardous airpollutants under section 112 (42 U.S.C.7412).

C. Review of Air Quality Criteria andStandards for O3

The last review of O3 air qualitycriteria and standards was completed inMarch 1993 with notice of a finaldecision not to revise the existingprimary and secondary standards (58 FR13008). The current primary andsecondary standards are each set at alevel of 0.12 ppm, with a 1–houraveraging time and a 1-expected-exceedance form, such that thestandards are attained when theexpected number of days per calendaryear with maximum hourly averageconcentrations above 0.12 ppm is equalto or less than 1, averaged over 3 years(as determined by 40 CFR part 50,Appendix H).1

The EPA initiated this current reviewof the air quality criteria and standardsin August 1992 with the development ofa revised Air Quality Criteria Documentfor O3 and Other PhotochemicalOxidants, henceforth the ‘‘CriteriaDocument.’’ Several workshops wereheld by EPA’s National Center forEnvironmental Assessment (NCEA) todiscuss health and welfare effectsinformation during the summer and fallof 1993. An external review draft of theCriteria Document made available to thepublic and to the CASAC in the springof 1994 was reviewed at a publicCASAC meeting held on July 20–21,1994. Based on comments made at themeeting, NCEA staff prepared a secondexternal review draft, which wasreviewed at a public CASAC meeting onMarch 21–22, 1995. At the samemeeting, the CASAC also reviewed draftportions of a staff paper prepared by theOAQPS, Review of National AmbientAir Quality Standards for O3:Assessment of Scientific and TechnicalInformation (henceforth, the ‘‘StaffPaper’’), focusing on health effects andthe primary NAAQS.2 Taking intoaccount CASAC and public comments,staff revised both documents and madenew drafts available for public andCASAC review during the summer of1995. The OAQPS staff also preparedand made available draft portions of theStaff Paper focusing on welfare effectsand the secondary standard.


A public CASAC meeting was held onSeptember 19–20, 1995, at which timeCASAC came to closure in its review ofthe draft Criteria Document and theprimary standard sections of the draftStaff Paper. In a November 28, 1995letter from the CASAC chair to theAdministrator, CASAC advised that thefinal draft Criteria Document ‘‘providesan adequate review of the availablescientific data and relevant studies of O3

and related photochemical oxidants’’(Wolff, 1995a). Further, in a November30, 1995 letter, CASAC advised theAdministrator that the primary standardportion of the draft Staff Paper‘‘provides an adequate scientific basisfor making regulatory decisionsconcerning a primary O3 standard’’(Wolff, 1995b). The final CriteriaDocument (U.S. EPA, 1996a) reflectsCASAC and public comments receivedat and subsequent to the September1995 CASAC meeting.

Based on comments on the Staff Paperfrom the September 1995 CASACmeeting, revisions were made to thesecondary standard sections of the StaffPaper, which were reviewed at a publicCASAC meeting held on March 21,1996. At that meeting and in asubsequent letter to the Administrator,CASAC concluded that the secondarystandard sections of the draft Staff Paper‘‘provide an appropriate scientific basisfor making regulatory decisionsconcerning a secondary O3 standard’’(Wolff, 1996). The final Staff Paper (U.S.EPA, 1996b) reflects CASAC and publiccomments received at and subsequent tothe September 1995 and March 1996meetings on the primary standard andsecondary standard sections,respectively.

On November 27, 1996 EPAannounced its proposed decision torevise the NAAQS for O3 (61 FR 65716,December 13, 1996, hereinafter‘‘proposal’’) as well as its proposeddecision to revise the NAAQS forparticulate matter (PM). In the proposal,EPA identified proposed revisions,based on the air quality criteria for O3,and solicited public comments onalternative primary and secondarystandards and on the proposed forms ofthe standards.

To ensure the broadest possiblepublic input on the O3 and PMproposals, EPA took extensive andunprecedented steps to facilitate thepublic comment process beyond thenormal process of providing anopportunity to request a hearing andreceiving written comments submittedto the rulemaking docket. The EPAestablished a national toll-freetelephone hotline to facilitate publiccomments on the proposed revisions to

the O3 and PM NAAQS, and on relatednotices dealing with the implementationof revised O3 and PM standards, as wellas a system for the public to submitcomments on the proposalselectronically via the Internet. Over14,000 calls and over 4,000 electronicmail messages were received throughthese channels. The public could alsoaccess key supporting documents(including the Criteria Document, StaffPaper, related technical documents andfact sheets) via the Internet.

The EPA also held several publichearings and meetings across thecountry to provide direct opportunitiesfor public comment on the proposedrevisions to the O3 and PM NAAQS andto disseminate information to the publicabout the proposed standard revisions.On January 14 and 15, 1997, EPA heldconcurrent, 2–day public hearings inBoston, MA, Chicago, IL, and Salt LakeCity, UT. A fourth public hearing,which focused primarily on PMmonitoring issues, was held in Durham,NC on January 14, 1997. Over 400citizens and organizations testifiedduring these public hearings. EPA alsoheld two national satellite telecasts toanswer questions on the standards andparticipated in meetings sponsored bythe Air and Waste ManagementAssociation on the proposed revisionsto the standards at more than 10locations across the country. Beyondthat, several EPA regional offices heldpublic meetings and workshops andparticipated in hearings that States andcities held around the country.

As a result of this intensive effort tosolicit public input, over 50,000 writtenand verbal comments were received onthe proposed revisions to the O3

NAAQS by the close of the publiccomment period on March 12, 1997.The major issues raised in thecomments are discussed throughout thepreamble of this final rule. Acomprehensive summary of allsignificant comments, along with EPA’sresponse to such comments (hereafter‘‘Response to Comments’’), can be foundin the docket for this rulemaking(Docket No. A–95–58).

The focus of this current review of theair quality criteria and standards for O3

and related photochemical oxidants ison public health and welfare effectsassociated with exposure to ambientlevels of tropospheric O3. TroposphericO3 is chemically identical tostratospheric O3, which is producedmiles above the earth’s surface andprovides a protective shield from excessultraviolet radiation. In contrast,tropospheric O3 at sufficientconcentrations has been associated withharmful effects due to its oxidative

properties and its presence in the airthat people and plants take up duringrespiratory processes. Ozone is notemitted directly from mobile orstationary sources but, like otherphotochemical oxidants, commonlyexists in the ambient air as anatmospheric transformation product.Ozone formation is the result ofchemical reactions of volatile organiccompounds (VOC), nitrogen oxides(NOx), and oxygen in the presence ofsunlight and generally at elevatedtemperatures. A detailed discussion ofatmospheric formation, ambientconcentrations, and health and welfareeffects associated with exposure to O3

can be found in the Criteria Documentand in the Staff Paper.

D. Summary of Proposed Revisions tothe O3 Standards

For reasons discussed in the proposal,the Administrator proposed to replacethe current 1–hour primary standard forO3 with an 8–hour standard set at 0.08ppm, which would be met at an ambientair quality monitoring site when the 3–year average of the annual third-highestdaily maximum 8–hour average O3

concentration is less than or equal to0.08 ppm. The proposal solicitedcomments on alternative 8–hourstandards set at 0.09 ppm, whichgenerally represents the continuation ofthe present level of protection, and 0.07ppm, which would be highlyprecautionary in nature, as well as onretaining the current primary standard.The proposal also solicited commentson alternative forms of the standard,specific data handling and roundingconventions used in determiningattainment with the standard, and issuesrelated to the communication of publichealth information.

With regard to the secondarystandard, the Administrator proposed toreplace the current 1–hour secondarystandard with one of two alternativestandards: either one set identical to theproposed primary standard or a newseasonal standard expressed as a sum ofhourly O3 concentrations greater than orequal to 0.06 ppm, cumulated over 12hours per day during the consecutive 3–month period of maximumconcentrations during the O3 monitoringseason, set at a level of 25 ppm-hour.The proposal solicited comments onthese two alternatives, as well as onspecific issues related to the form of aseasonal standard and on an enhancedrural air quality monitoring network.


3 ‘‘Acute health effects’’ of O3 are defined as thoseeffects induced by short-term and prolongedexposures to O3. Examples of these effects arefunctional, symptomatic, biochemical, andphysiologic changes.

4 ‘‘Chronic health effects’’ of O3 are defined asthose effects induced by long-term exposures to O2.Examples of these effects are structural damage tolung tissue and accelerated decline in baseline lungfunction.

II. Rationale for the Primary Standard

A. Introduction

1. Overview . This notice presents theAdministrator’s final decision regardingthe need to revise the current primaryO3 standard, and, more specifically,regarding the averaging time, level, andform of a new primary standard toreplace the current 1–hour standard.This decision is based on a thoroughreview, in the Criteria Document, of thescientific information on human healtheffects associated with exposure toambient levels of O3, includingevaluation of key studies publishedthrough 1995. This decision also takesinto account:

(1) Staff Paper assessments of themost policy-relevant information in theCriteria Document and analyses ofhuman exposure and risk, presented inthe Staff Paper and supporting technicalreports.

(2) CASAC advice andrecommendations, as reflected indiscussions of drafts of the CriteriaDocument and Staff Paper at publicmeetings, in separate written comments,and in CASAC’s letters to theAdministrator.

(3) Public comments received duringthe development of these documents,either in connection with CASACmeetings or separately.

(4) Extensive public commentsreceived on the proposal regarding theprimary O3 standard.

After taking this information andcomments into account and for thereasons discussed below in this unit, theAdministrator concludes that revisionsto the current primary standard toprovide increased public healthprotection are appropriate at this time toprotect public health with an adequatemargin of safety. Further, theAdministrator determines that it isappropriate to establish a revised 8–hour, 0.08 ppm primary standard witha form based on the 3–year average ofthe annual fourth-highest dailymaximum 8–hour average O3

concentrations measured at eachmonitor within an area.

As discussed more fully below in thisunit, the rationale for the final decisionregarding the O3 primary NAAQSincludes consideration of:

(1) Health effects information toinform judgments as to the likelihoodthat exposures to ambient O3 result inadverse health effects for exposedindividuals.

(2) Insights gained from humanexposure and risk assessments toprovide a broader perspective forjudgments about protecting public

health from the risks associated with O3

exposure.(3) Specific conclusions with regard

to the elements of a standard (i.e.,averaging time, level, and form) that,taken together, would be appropriate toprotect public health with an adequatemargin of safety.

(4) Alternative views of thesignificance of the effects and factors tobe considered in policy judgments aboutthe appropriate elements of thestandard.

The health effects information andhuman exposure and risk assessmentswere summarized in the proposal andare only briefly outlined below. Morefully discussed in the following units ofthis preamble is the Administrator’srationale, in light of key issues raised inpublic comments, for concluding that itis appropriate to revise the specificelements of the current standardincluding averaging time (Unit II.B.1.),level (Unit II.B.2.), and form (UnitII.B.3.). Finally, the related subject ofthe communication of public healthinformation, and the public commentsreceived on this subject, aresummarized in Unit II.C.

2. Health effects information. The lastreview of the air quality criteria for O3

included an evaluation of key studiespublished through early 1989 and wasthe basis for EPA’s 1993 decision not torevise the primary standard at that time.However, in recognition of the largenumber of new studies, particularly on6– to 8–hour exposures to O3, that hadbecome available since early 1989 buthad not undergone rigorous assessmentand review by CASAC, the EPA madeclear in the 1993 final decision noticethat it would proceed with the nextreview as rapidly as possible to considerthis new information. Thus, the currentreview of health effects informationfocused on a large body of informationpublished since 1989 that would lead toa more informed decision than waspossible in 1993 as to whether an O3

primary standard with a longeraveraging time was appropriate toprotect public health.

The proposal reviewed the humanhealth effects associated with exposureto ambient levels of O3 based on anintegrative assessment of humanclinical, epidemiological, and animaltoxicological studies available through1995, as assessed in the CriteriaDocument and Staff Paper. Based onthis information, an array of healtheffects has been attributed to short-term(1 to 3 hours), prolonged (6 to 8 hours),and long-term (months to years)exposures to O3.

Acute health effects3 are induced byshort-term exposures to O3 (observed atconcentrations as low as 0.12 ppm),generally while individuals are engagedin moderate or heavy exertion, and byprolonged exposures to O3 (observed atconcentrations as low as 0.08 ppm),typically while individuals are engagedin moderate exertion. Moderate exertionlevels are more frequently experiencedby individuals than heavy exertionlevels. The acute health effects includetransient pulmonary function responses,transient respiratory symptoms, effectson exercise performance, increasedairway responsiveness, increasedsusceptibility to respiratory infection,increased hospital admissions andemergency room visits, and transientpulmonary inflammation. Based inparticular on new information availablesince the last review of the air qualitycriteria for O3 was completed, suchacute health effects have been observedfollowing prolonged exposures atmoderate levels of exertion atconcentrations of O3 as low as 0.08ppm. Groups at increased risk ofexperiencing such effects include activechildren and outdoor workers whoregularly engage in outdoor activitiesand individuals with preexistingrespiratory disease (e.g., asthma, chronicobstructive lung disease). Further, it isrecognized that some individuals areunusually responsive to O3 and mayexperience much greater functional andsymptomatic effects from exposure to O3

than the average individual.With regard to chronic health effects4,

the collective data from studies oflaboratory animals and humanpopulations have many ambiguities, butprovide suggestive evidence of sucheffects in humans. It is clear fromtoxicological data that O3-induced lunginjury is roughly similar across species(including monkeys, rats, and mice)with responses that are concentrationdependent. The currently availableinformation provides at least abiologically plausible basis forconsidering the possibility that repeatedinflammation associated with exposureto O3 over a lifetime may result insufficient damage to respiratory tissuesuch that individuals later in life mayexperience a reduced quality of life,


5 ‘‘Exposures of concern’’ refer throughout toexposures at and above 0.08 ppm, 8–hour average,at which a range of health effects have beenobserved in controlled human studies, but forwhich data were too limited to allow forquantitative risk assessment.

6 This study is one of several studies, mainlyconducted in the northeastern portion of the UnitedStates and southeastern Canada, reporting excessdaily respiratory-related hospital admissionsassociated with elevated O3 levels within thegeneral population and, more specifically, forindividuals with asthma.

7 The analyses were conducted for the at-riskpopulation of outdoor children, the group with thehighest exposures and risks. Outdoor children arethe subset of children between the ages of 6 and 18years old who tend to be active outdoors, andinclude approximately over 30 percent to 45

although such relationships remainhighly uncertain.

EPA’s consideration of this healtheffects information necessarily includedjudgments with respect to when thesephysiological effects become sosignificant that they should be regardedas adverse to the health of individualsexperiencing the effects. In makingthese judgments, the Administratorlooked to guidelines published by theAmerican Thoracic Society (1985) andthe advice of CASAC. The proposalsummarized the criteria and reasoningfor EPA’s judgments on this issue, uponwhich the CASAC panel expressed aconsensus view that these ‘‘criteria forthe determination of an adversephysiological response was reasonable’’(Wolff, 1995b). The criteria take intoaccount the degree of severity of theeffects; the likelihood that the effectswould interfere with normal activity forindividuals with impaired respiratorysystems or active healthy individuals;the likelihood that the effects wouldresult in additional or more frequent useof medication, medical treatment, oremergency room visits for individualswith impaired respiratory systems; andthe implications of single or repeatedoccurrences of the effects for anindividual.

Some commenters raised concernsregarding the criteria used by EPA tomake determinations as to when effectsbecome adverse, citing CASAC’s closureletter (Wolff, 1995b) stating that ‘‘therewas considerable concern that thecriteria for grading physiological andclinical responses to O3 was confusingif not misleading.’’ These concerns withthe draft criteria were discussed atlength during a public CASAC meeting,resulting in very specific agreements asto how to revise the draft criteria so asto be consistent with CASAC’s advice(Transcript of CASAC meeting,September 19–20, 1995, pp. 242–248).Having reached such specificagreement, CASAC advised that furtherreview of the final version of thesecriteria, subsequently incorporated inboth the final Criteria Document andStaff Paper, was unnecessary.

Other commenters have questionedwhether judgments made in this revieware consistent with those made in thelast review with regard to whenphysiological and clinical effectsbecome adverse to individualsexperiencing such effects. Specifically,the commenters focused on thejudgment stated in the 1993 finaldecision notice (58 FR 13008, March 9,1993) that ‘‘lesser effects associated with[1– to 3–hour] exposure to O3 in therange of 0.12 ppm to 0.15 ppm observedin the controlled human studies did not

constitute adverse effects for purposesof section 109 of the Act.’’ The ‘‘lessereffects’’ referred to in that noticeinvolved responses of a maximumdecrease in lung function [as measuredby forced expiratory volume in 1 second(FEV1)] of from 9 percent to 16 percentfor the most sensitive individualsexposed in this range, with few, if any,symptoms. The EPA notes that thisjudgment is, in fact, consistent withjudgments presented in the 1996proposal, which identify moderate andlarge lung function decrements (asreflected in EPA’s risk assessment byFEV1 decreases of ≥ 15 percent and ≥ 20percent, respectively, with the mostsensitive individuals experiencing FEV1

decreases as large as 40 percent to 50percent at 6– to 8–hour exposures in therange of 0.08 ppm to 0.10 ppm incontrolled human studies), andmoderate to severe symptoms as beingadverse.

3. Exposure and risk assessments. Toput judgments about health effects thatare adverse for individuals into abroader public health context, EPAconducted quantitative assessments toestimate O3 exposures and related risksfor the general population and two at-risk groups, ‘‘outdoor children’’ and‘‘outdoor workers,’’ living in ninerepresentative U.S. urban areas. Thisbroader context included consideration,to the extent possible, of the size of theparticular population groups identifiedas at risk for various effects, theestimated number of people within at-risk groups likely to experience O3-related adverse effects, the estimatednumber of occurrences of such effects,and the estimated number of peoplewho would experience exposures ofconcern5 associated with various airquality scenarios representingattainment of the current and alternative8–hour standards. Consideration wasalso given to the kind and degree ofuncertainties inherent in assessing suchexposures and risks. Suchconsiderations provided a basis forjudgments discussed in the proposalabout the levels of exposure and riskassociated with the current andalternative standards, which helpedinform judgments about the adequacy ofpublic health protection afforded by thecurrent and alternative standards.

Risk estimates were developed forthose effects for which sufficientconcentration-response information wasavailable from studies evaluated in the

Criteria Document, including adverselung function and respiratory symptomresponses. In a separate analysis, excessrespiratory hospital admissions forindividuals with asthma associated withattainment of alternative standards werealso estimated, using a risk model forthis health endpoint based on theresults of an epidemiological study inNew York City (Thurston et al., 1992)for which adequate air qualityinformation was available to assesspopulation risk6. These quantitative riskestimates (for that subset of O3-relatedeffects for which information issufficient to conduct such quantitativeanalyses) add to our understanding ofthe broader array of health effects thatare associated with exposure to O3 butfor which quantitative risk estimatescould not be developed.

The methodology, results, and keyobservations from these assessmentswere presented in the proposal. TheEPA believes, and CASAC concurred,that the models selected to estimateexposure and risk were appropriate andthat the methods used to conduct thehealth risk assessment for adverse lungfunction and respiratory symptomresponses represent the state of the art.Nevertheless, the Administrator andCASAC recognized that there are manyuncertainties inherent in such analyses,and that not all uncertainties inherent insuch analyses could be quantified andreflected in ranges of risk estimates(Wolff, 1995b), as discussed in theproposal and the referenced technicalsupport documents.

The exposure and risk assessmentsavailable at the time of proposal hadbeen conducted to evaluate the O3

exposures and risks associated withattainment of the current 1–hourstandard and various alternative 8–hourstandards under consideration early inthe standards review process when theassessments were initiated. The EPAand CASAC recognized at that time thatadditional alternative standards mightneed to be analyzed later in the reviewprocess. Upon deciding to propose astandard with a concentration-basedform in the Fall of 1996, EPA staffinitiated supplemental analyses toestimate exposures and risks7 for the


percent of all children in this age group in the nineurban areas analyzed.

8 These changes primarily focused on the airquality data used in the exposure analysis and onthe air quality adjustment procedures used tosimulate ambient O3 concentrations uponattainment of alternative standards.

9 This review focused only on a standard for O3,as the most appropriate surrogate for photochemicaloxidants.

specific standard to be proposed andalternative standards on which theproposal solicited comment. Inconducting these supplementalanalyses, several technical changes weremade based on insights gained from theinitial analyses.8 The supplementalassessment (Richmond, 1997) wasplaced in the docket and on the TTN onFebruary 12, 1997, and its availabilitywas announced in the Federal Registernotice extending the public commentperiod on the proposal, providing thepublic the opportunity to comment onthe supplemental assessment (61 FR7743, February 20, 1997).

Key observations and results from theinitial and supplemental exposure andrisk assessments that are most pertinentto the decision to revise the currentprimary standard are highlighted in thefollowing unit, together with discussionof the key issues raised in publiccomments on the methodology andpublic health implications of theseassessments.

B. Elements of the Primary Standard

In selecting a primary standard for O3,the Administrator must specify:Averaging time, O3 concentration (i.e.,level), and form (i.e., the air qualitystatistic to be used as a basis fordetermining compliance with thestandard).9 All three of these elementsare necessary to define a standard andto determine the degree of public healthprotection afforded by the standard. Theproposal outlined the key factorsconsidered in selecting each of theseelements for the proposed standard, aswell as the range of options for eachelement on which the EPA solicitedcomment. The factors reflect anintegration of information on acute andchronic health effects associated withexposure to ambient O3; expertjudgments on the adversity of sucheffects for individuals; and policyjudgments, informed by air quality andexposure analyses and quantitative riskassessment when possible, as to thepoint at which risks would be reducedsufficiently to achieve protection ofpublic health with an adequate marginof safety.

This approach to selecting a primarystandard was endorsed by CASAC(Wolff, 1995b), particularly through its

advice to the Administrator that ‘‘EPA’srisk assessments must play a central rolein identifying an appropriate level’’ andits recognition that ‘‘the selection of aspecific level and [form] is a policyjudgment.’’ Further, it was theconsensus view of CASAC that theranges of 8–hour average levels (0.07 to0.09 ppm) and forms (concentration-based forms that generally allow for 1 to5 exceedances) on which the proposalsolicited comment were appropriate.

The following discussion focusesprimarily on those considerations thatwere most influential in theAdministrator’s final decisions on theseelements, taking into account thecomments received on the range ofoptions identified in the proposal.

1. Averaging time. In proposing tochange the averaging time of theprimary standard from 1 to 8 hours, theAdministrator was concurring with theunanimous recommendation of CASAC(Wolff, 1995b) ‘‘that the present 1–hourstandard be eliminated and replacedwith an 8–hour standard,’’ and thatmore research is needed to resolveuncertainties about potential chroniceffects before appropriate considerationcan be given to establishing a long-term(e.g., seasonal or annual) primarystandard. The Administrator’s proposeddecision was supported by the followingkey observations and conclusions:

(1) The 1–hour averaging timespecified in the current NAAQS wasoriginally selected primarily on thebasis of health effects associated withshort-term (i.e., 1– to 3–hour) exposures,with qualitative consideration given topreliminary information on potentialassociations with longer exposureperiods.

(2) Substantial new health effectsinformation available for considerationin this review demonstrates associationsbetween a wide range of health effectsand prolonged (i.e., 6– to 8–hour)exposures below the level of the current1–hour NAAQS.

(3) Results from the quantitative riskanalyses show that attaining a standardwith a 1-hour averaging time reducesthe risk of experiencing health effectsassociated with both 1–hour and 8–hourexposures. Likewise, attaining an 8–hour standard reduces the risk ofexperiencing health effects associatedwith both 8–hour and 1–hourexposures. Thus, reductions in risksfrom both short-term and prolongedexposures can be achieved through aprimary standard with an averagingtime of either 1 or 8 hours. As a result,establishment of both 1–hour and 8–hour standards would not be necessaryto reduce risks associated with the fullrange of observed acute health effects.

(4) The 8–hour averaging time is moredirectly associated with health effects ofconcern at lower O3 concentrations thanis the 1–hour averaging time. It was thusthe consensus of CASAC ‘‘that an 8–hour standard was more appropriate fora human health-based standard than a1–hour standard.’’ (Wolff, 1995b)

(5) While there is a large animaltoxicology database providing clearevidence of associations between long-term (e.g., from several months to years)exposures and lung tissue damage, withadditional evidence of reduced lungelasticity and accelerated loss of lungfunction, there is no correspondingevidence for humans. Moreover, thestate of the science has not progressedsufficiently to permit quantitativeextrapolation of the animal-studyfindings to humans. Thus, theAdministrator concluded thatconsideration of a separate long-termprimary O3 standard is not appropriateat this time. As discussed below,however, the Administrator consideredthe possibility of long-term effects inselecting the level of an 8–hourstandard, which will provide protectionagainst such effects to the extent theymay occur in humans, by loweringoverall air quality distributions and,thus, reducing cumulative long-termexposures.

The public comments reflect broadsupport for a standard with an 8–houraveraging time, either alone or inconjunction with a 1–hour standard.This support was typically based onreferences to:

(1) Evidence of health effects from 6–to 8–hour exposures to O3

concentrations down to 0.08 ppm,which are lower than thoseconcentrations that have induced sucheffects after 1– to 3–hour exposures, andwhich are lower than the 0.12 ppm levelof the current standard.

(2) Analyses indicating that an 8–hourstandard would limit both 1– and 8–hour exposures.

(3) CASAC’s unanimous agreementthat the current 1–hour standard shouldbe replaced by an 8–hour standard. Inconsidering the adequacy of the current1–hour standard alone in light of thehealth effects evidence, somecommenters have highlighted thestatement in the Criteria Document thatthere is ‘‘strong evidence that ambientexposures to O3 can cause significantexacerbations of preexisting respiratorydisease in the general public atconcentrations below 0.12 ppm.’’ (U.S.EPA, 1996a, p. 7–171)

Commenters expressing support foran 8–hour averaging time included notonly those who supported a level ofpublic health protection consistent with


10 More precisely, exposures at and above 0.08ppm refers to estimates of exposures to O3

concentrations ≥ 0.081 ppm from the exposureassessment.

11 In terms of the percent of outdoor childrenestimated to be exposed to O3 concentrations at andabove 0.08 ppm while engaged in moderateexertion, the current 1–hour standard results in arange across the seven nonattainment areas ofapproximately 0.3 percent to 24 percent of suchchildren, whereas alternative 8–hour standards, atthe proposed level of 0.08 ppm, result in asignificantly more uniform degree of protection,with ranges of approximately 2 percent to 9 percent,third-highest concentration form, and 3 percent to11 percent, fifth-highest concentration form, acrossthe areas.

or greater than that reflected by EPA’sproposed standard, but also many whodisagreed for various reasons with theneed for increased public healthprotection beyond that provided by thecurrent standard. Of those supporting an8–hour averaging time but notsupporting the need for increasedprotection, some expressed the viewthat the averaging time of a health-basedstandard should be consistent with theexposures of most concern, while otherswere simply neutral between thechoices of retaining the current 1–hourstandard and replacing it with an‘‘equivalent’’ 8–hour standard.

The EPA agrees with theconsiderations raised by thosecommenters who favor an 8–hourstandard. Further, in considering theappropriateness of an 8–hour standardas compared to a 1–hour standard, EPAalso notes the results of its exposure andrisk assessments which show variabilityacross the nine urban areas analyzedwith regard to the extent to which thecurrent 1–hour standard, and alternative8–hour standards, limit 8–hourexposures of concern and associatedrisks of adverse health effects. As notedin the proposal and in the supplementalrisk assessment, there is much greatervariability across urban areas,particularly in looking at the sevencurrent nonattainment areas examined,in the extent to which the current 1–hour standard limits such exposures ofconcern and risks than for thealternative 8–hour standards. Forexample, the updated assessmentestimates that the current 1–hourstandard results in 8–hour exposures ofconcern at and above 0.08 ppm10 thatvary by almost two orders of magnitudeacross these areas. In contrast,alternative 8–hour standards at theproposed level of 0.08 ppm result inestimated 8–hour exposures of concernand risks that are much moreconsistent.11 In EPA’s view, the fact thatan averaging time of 8 hours results ina significantly more uniformlyprotective national standard than thecurrent 1–hour standard is an important

public health policy consideration thatsupports the selection of an 8–houraveraging time.

Those commenters who did notsupport EPA’s proposal for an 8–houraveraging time generally did not supportany revision to the current standard.These commenters predominantlyfocused on two basic points: Thegenerally improving trends in air qualityunder the current standard andassociated air quality managementprograms, which, commenters argued,suggest that there is no need for EPA toadopt any more stringent standard; andobservations made in CASAC’s closureletter (Wolff, 1995b) with regard toEPA’s risk assessment notdemonstrating any ‘‘bright line’’threshold of effects or acceptable risk.With regard to the first issue, EPAagrees that air quality trends areimproving as a consequence of ongoingcontrol programs designed to attain thecurrent NAAQS. The EPA does not,however, believe that these trendsrelieve the Agency of its statutorymandate to review and, if appropriate,revise the NAAQS on the basis of thebest available scientific evidence toestablish standards that protect publichealth with an adequate margin ofsafety. The fact that current controlprograms are resulting in progresstoward improving air quality doessuggest that it is important to ensurethat such progress is maintained duringany transition to a revised standard.

With regard to the second issue,commenters very frequently quotedfrom the CASAC closure letter (Wolff,1995b) stating ‘‘that there is no brightline’ which distinguishes any of theproposed standards (either the level orthe number of allowable exceedances)as being significantly more protective ofpublic health’’ and that ‘‘the selection ofa specific level and number of allowableexceedances is a policy judgment.’’These commenters have variouslyinterpreted these statements as aCASAC consensus that the differencesin the public health protection affordedby any of the alternative standards weretoo small to be important from a publichealth perspective, not statisticallysignificantly different, or simply notdifferent at all. Based on theseinterpretations, the commenters arguedthat it is not appropriate to revise thestandard in any way, because a revisedstandard would result in disruption toongoing programs, additional planningrequirements, and increasedimplementation costs, but wouldprovide no or only very littleimprovement in public healthprotection.

The EPA believes that thesecommenters have misconstrued or toonarrowly interpreted CASAC’s advice tothe Administrator by not consideringthe entire range of views andrecommendations included in itsclosure letter. Specifically, CASACbegan its summary of recommendationsto the Administrator (Wolff, 1995b) bystating that ‘‘[t]he Panel was inunanimous agreement that the present1–hour standard be eliminated andreplaced with an 8–hour standard.’’This agreement was based on ‘‘theconsensus of the Panel that an 8–hourstandard was more appropriate for ahuman health-based standard than a 1–hour standard.’’ Thus, CASAC wasunequivocal in its advice to theAdministrator with regard to whichaveraging time the health effectsevidence more strongly supports. Whilesome commenters have also quotedstatements by individual Panel membersat CASAC meetings suggesting thatchoosing between a 1– or 8–houraveraging time is a ‘‘policy’’ choice,these individual statements during thecourse of CASAC’s review do notcontradict nor supersede the clear andunanimous agreement of CASAC onaveraging time as conveyed to theAdministrator in its closure letter.

In considering these comments, EPAalso believes it is important to put intoa public health perspective CASAC’sobservations about the differencesamong alternative standards inprotecting the public from the healtheffects that were quantitativelyestimated in EPA’s risk assessment. Inthe closure letter (Wolff, 1995b), CASACobserved that ‘‘the differences in thepercent of outdoor children ***responding between the presentstandard and the most stringentproposal *** are small and their rangesoverlap for all health endpoints.’’ Mostimportantly, EPA notes that the primarystandard would provide protection froma broader array of health effects than itwas possible to consider in itsquantitative risk assessment. Thisperspective is clearly shared inparticular by those CASAC panelmembers who personally favored a levelor range of levels that included theproposed level of 0.08 ppm, in that theclosure letter characterizes their viewsas reflecting, in part, their ‘‘concern overthe evidence for chronic deep lunginflammation from the controlledhuman and animal exposure studies.’’While the risk of this effect, as well asother effects related to 6– to 8–hourexposures in the Criteria Document andStaff Paper (including increased airwayresponsiveness, impairment of host


12 The EPA recognizes this possibility existsespecially in the very few areas with unusually‘‘peaky’’ air quality patterns (i.e., in which the ratioof the 1– and 8–hour average design values for thecurrent and proposed standards is greater than 1.5).

defenses suggesting an increasedsusceptibility to respiratory infection,and increased emergency room visits,doctor visits, and frequency ofmedication use by individuals withimpaired respiratory systems) could notbe quantitatively estimated in EPA’s riskassessment, EPA believes thatconsideration of these effects isnevertheless important in making publichealth policy judgments.

Further, in interpreting CASAC’sstatements on EPA’s risk assessmentreport (Whitfield et al., 1996) that thereis no ‘‘bright line’’ which distinguishesany of the standards as being‘‘significantly’’ more protective, and thatthe ‘‘ranges overlap,’’ EPA notes thatthere are statistically significantdifferences in the estimated risks for thestandards analyzed with 1- and 5-exceedance forms. This information waspresented to CASAC at its September1995 meeting (CASAC meetingtranscript, September 19–20, 1995, pp.108–109). Further, EPA again notes thatwhether one judges the differences to besignificant or small can depend onwhether one focuses on percentages, asCASAC’s letter did, or on total numbersof times that children or other at-riskindividuals experience such effects. Theoverlap in the ranges of risk referred toin the CASAC letter reflect differencesamong urban areas used in EPA’s riskanalysis (e.g., air quality, exposurepatterns, environmental factors), notrandom uncertainties in risk estimateswithin any given urban area. Thus, thefact that the ranges overlap does notmean that there are no real orstatistically significant differences inprotection among alternative standards.To the extent that the quoted statementsfrom CASAC’s closure letter are read asimplying that CASAC considered thedifferences not to be statisticallysignificant (or that there are nodifferences at all in the protectionafforded by the alternative standards),EPA disagrees with that reading.

Another group of commenters, whilesupporting an 8–hour standard,specifically opposed replacing thecurrent 1–hour standard with an 8–hourstandard, but favored instead both 8–hour and 1–hour standards. Thesecommenters generally felt that a greaterdegree of public health protection thanthat provided by the proposed standardwas warranted, and that standards basedon both averaging times were necessaryto provide the requisite protection from1– and 8–hour exposures of concern.These commenters generally argued thatan 8–hour standard alone could stillallow for high 1–hour exposures ofconcern, or that the retention of thecurrent 1–hour standard was critical to

maintaining current pollution controlmeasures. As an initial matter, EPA isdelaying revocation of the 1–hourstandard to ensure an effectivetransition to the 8–hour standard, asdiscussed in Unit II.B.4 of thispreamble. While EPA agrees that it ispossible that an 8–hour standard alonecould allow for high 1–hour exposuresof concern, at and above 0.12 ppm,12

EPA’s exposure assessments estimatethat alternative 8–hour standards, at theproposed level of 0.08 ppm but withdifferent forms, would be very effectivein limiting 1–hour exposures, andgenerally even more effective in limiting1–hour exposures of concern than is thecurrent 1–hour standard. Morespecifically, the updated assessmentestimates that upon attainment ofalternative 8–hour, 0.08 ppm standards,with forms ranging up to the fifth-highest concentration form, less than 0.1percent of outdoor children are likely toexperience any 1–hour exposuresgreater than 0.12 ppm while at heavyexertion levels in four to seven of thenine urban areas analyzed, whereas thisis true for only two of the nine areasupon attainment of the current 1–hourstandard. In all nine areas both thecurrent and alternative 8–hour, 0.08ppm standards are estimated to limitsuch exposures to less than 1 percent ofthe outdoor children. Thus, EPAconcludes that an 8–hour averaging timedoes effectively limit both 1– and 8–hour exposures of concern.

For the reasons discussed above inthis unit, and after taking into accountthe range of views expressed in thepublic comments, the Administratorfinds that replacing the current 1–hourstandard with an 8–hour standard, incombination with the decisions on leveland form described below, isappropriate to provide adequate andmore uniform protection of publichealth from both short-term (1 to 3hours) and prolonged (6 to 8 hours)exposures to O3 in the ambient air.

2. Level. Taken together, the level andform of the standard, for a givenaveraging time, determine the degree ofpublic health protection afforded by thestandard. Consideration of the level ofthe standard discussed in this unit ofthe preamble reflects a recognition ofthis linkage between level and form(discussed separately below in UnitII.B.3).

The Administrator’s decision topropose the level of an 8–hour primaryO3 standard at 0.08 ppm, and to solicit

comment on alternative levels,necessarily reflected a recognition, asemphasized by CASAC, that it is likelythat ‘‘O3 may elicit a continuum ofbiological responses down tobackground concentrations’’ (Wolff,1995b). Thus, in the absence of anydiscernible threshold, it is not possibleto select a level below which absolutelyno effects are likely to occur. Nor doesit seem possible, in the Administrator’sjudgment, to identify a level at which itcan be concluded with confidence thatno ‘‘adverse’’ effects are likely to occur.In such a case, as CASAC has advised,the traditional paradigm for standard-setting cannot be applied in the usualway, and assessments of risk ‘‘must playa central role in identifying anappropriate level’’ (Wolff, 1995b). Thus,the Administrator’s task became one ofattempting to select a standard level thatwould reduce risks sufficiently toprotect public health with an adequatemargin of safety, since a zero-riskstandard is neither possible nor requiredby the Act. In this and other NAAQSreviews the CASAC has generallyrecognized that the selection of specificstandards requires that theAdministrator make public healthpolicy judgments in addition todeterminations of a strictly scientificnature. The Administrator’s publichealth policy judgment on the level ofthe proposed standard was framed bythe considerations discussed above inthis unit and informed by the followingkey observations and conclusions:

(1) During the last review of the O3

criteria and standards, CASACconcluded that the existing 1–hourstandard set at 0.12 ppm O3 provided‘‘little, if any, margin of safety,’’ and thatthe upper end of the range ofconsideration for a 1–hour standardshould be 0.12 ppm (McClellan, 1989).In addition, several members of theCASAC panel recommended thatconsideration should be given to a lower1–hour level of 0.10 ppm to offer someprotection against effects for whichthere was preliminary information atthat time of associations with 8–hourexposures to O3.

Regarding currently availableevidence of O3-related effects:

(2) Based on a significant body ofinformation available since the lastreview, there is now clear evidence fromhuman clinical studies that O3 effects ofconcern are associated with the 6– to 8–hour exposures tested. Studies weredone at 6– to 8–hour exposure levels of0.12, 0.10, and 0.08 ppm. This includesevidence of the following statisticallysignificant responses at 6– to 8–hourexposures to the lowest concentrationevaluated, 0.08 ppm O3, at moderate


13 The upper end of this range, 3-expected-exceedances, was based on air quality comparisons,since risk estimates were only available at the timeof proposal for the 1– and 5-expected-exceedance

forms of a 0.09 ppm standard. This range isconsistent with the results of the updated riskassessment.

exertion: lung function decrements,respiratory symptoms (e.g., cough, painon deep inspiration), nonspecificbronchial responsiveness, andbiochemical indicators of pulmonaryinflammation. Field studies provideevidence of similar functional andsymptomatic effects at ambient O3

exposures that are consistent with theclinical findings. Laboratory animalstudies provide supporting evidence ofO3-induced biochemical indicators ofinflammation and functional changes.

(3) Numerous epidemiological studieshave reported excess hospitaladmissions and emergency departmentvisits for respiratory causes (forasthmatic individuals and the generalpopulation) attributed primarily toambient O3 exposures, including O3

concentrations below the level of thecurrent standard, with no discerniblethreshold at or below this level. Thebiological plausibility of attributingsuch effects to ambient O3 exposures issupported by human studies showingincreased nonspecific bronchialresponsiveness, laboratory animalstudies showing pulmonary changesthat decrease the effectiveness of thelung’s defenses against bacterialrespiratory infections, and thereasonable anticipation that O3

exposures also increase the risk ofrespiratory infections in humans, basedon the many similarities betweenanimal and human defensemechanisms.

(4) Long-term laboratory animalstudies suggest that changes in lungbiochemistry and structure may, undercertain circumstances, becomeirreversible, although it is unclearwhether long-term exposures to ambientO3 levels result in similar chronic healtheffects in humans.

Regarding the types and severity ofO3-induced physiological effects that areconsidered to be adverse to the healthstatus of individuals experiencing sucheffects:

(5) With regard to lung functiondecrements and respiratory symptoms,the Administrator recognized that theseO3-induced effects are transient andreversible, and concluded that theextent to which such effects are adverseto the health status of an individualdepends upon the severity, duration,and frequency with which an individualexperiences such effects throughout theO3 season. While group mean responsesin clinical studies at the lowestexposure level tested of 0.08 ppm aretypically small or mild in nature,responses of some sensitive individualsare sufficiently severe and extended induration to be considered adverse. Thiswould especially be true to the extent

that those individuals likely toexperience such effects would, onaverage, experience them several timesa year.

(6) With regard to increased hospitaladmissions and emergency room visits,the Administrator judged that sucheffects are clearly adverse toindividuals.

(7) With regard to pulmonaryinflammation, the Administratorrecognized that singular occurrences ofinflammation are likely reversible andpotentially of little health significance.On the other hand, based on laboratoryanimal studies, repeated inflammatoryresponses associated with exposure toO3 over a lifetime have the potential toresult in damage to respiratory tissuesuch that individuals later in life mayexperience a reduced quality of life.Furthermore, there is the possibility thatrepeated pulmonary inflammatoryresponses could adversely affectasthmatic individuals by resulting inincreased medication use, medicaltreatment, and/or emergency room visitsand hospital admission. Such effects inasthmatics are of special concernparticularly in light of the growingasthma problem in the United Statesand the increasing rates of asthma-related mortality and hospitalizations,especially among children in generaland black children in particular. WhileO3 has not been shown to cause asthma,the available evidence suggests that O3

may exacerbate asthma. Accordingly,the Administrator judged that repeatedexposures to O3 levels that produceinflammation of the lungs are adverse toindividuals likely to experience suchexposures over long periods of time.

The Administrator considered theresults of the exposure and risk analysesand the following key observations andconclusions from these analyses inputting effects considered to be adverseto individuals into a broader publichealth perspective and in makingjudgments about the level of a standardthat would reduce risk sufficiently toprotect public health with an adequatemargin of safety:

(8) The median risk estimates forrespiratory functional and symptomaticeffects, as well as for excess hospitaladmissions of asthmatics for respiratorycauses, are approximately the same oronly marginally smaller for some of the8–hour, 0.09 ppm standard optionsevaluated (including those with formsranging from 1- to 3-expected-exceedances13) as compared to the

current 1–hour, 0.12 ppm NAAQS (riskestimates are somewhat larger for an 8–hour, 0.09 ppm, 5-expected-exceedancestandard as compared to those for thecurrent NAAQS).

(9) Within any given urban area,statistically significant reductions inexposure and risk associated withrespiratory functional and symptomaticeffects result from alternative 8–hourstandards as the level changes from 0.09ppm to 0.08 ppm to 0.07 ppm. Thesereductions represent differences ofhundreds of thousands of times thatchildren in the nine urban areasincluded in the analysis would likelyexperience such effects under the rangeof alternative standards consideredrelative to the current standard. Thereare significant uncertainties in suchquantitative estimates, however, andthere is no break point or bright line thatdifferentiates between acceptable andunacceptable risks within this range.

(10) Similarly, reductions in hospitaladmissions for respiratory causes forasthmatic individuals and the generalpopulation are estimated to occur witheach change in the level of the standardfrom 0.09 ppm to 0.08 ppm to 0.07 ppm.However, hospital admissions forasthmatic individuals associated withambient O3 exposures within the rangeof standard levels under considerationrepresent a relatively small fraction ofthe total respiratory-related hospitaladmissions for asthmatics over the O3

season.(11) Estimated exposures to O3

concentrations at and above 0.08 ppm(at which increased nonspecificbronchial responsiveness, decreasedpulmonary defense mechanisms, andindicators of pulmonary inflammationhave been observed in humans) whileengaged in moderate exertion areessentially zero at the 0.07 ppmstandard level (with a 1-expected-exceedance form) for the sevennonattainment areas evaluated in theexposure analyses for the at-riskpopulation of outdoor children. Suchexposures of outdoor children increaseto approximately 0 to 1 percent at the0.08 ppm standard level, while theestimated range at the 0.09 ppmstandard level increases toapproximately 3 to 7 percent of outdoorchildren for these areas.

(12) While recognizing that sensitiveindividuals may experience adverse buttransient effects with a standard set at0.08 ppm, no CASAC panel membersupported selection of 0.07 ppm as thelevel of a primary standard. Of the


14 These updated risk estimates in terms of thepercentage of outdoor children in the nine urbanareas are roughly comparable to the range oforiginal estimates presented in Table 1 of theproposal for 1- and 5-expected-exceedance forms ofthe standards.

15 Approximately 3.1 million outdoor childrenreside in these nine urban areas.

members who expressed their personalviews, three indicated a preference fora level of 0.08 ppm, one for a range of0.08 to 0.09 ppm, three for a level of0.09 ppm (with one of the threeexpressing a preference for selecting aform that would result in equivalentprotection to the current standard), andone for a range of 0.09 to 0.10 ppm,associated with public advisories for O3

levels at and above 0.07 ppm. OtherCASAC panel members also expressedsupport for such public notices oradvisories reflecting potential effects forextremely sensitive individualsassociated with O3 levels as low as 0.07ppm.

These observations and conclusionsresulted in the Administrator focusingin particular on the alternative levels of0.08 ppm and 0.09 ppm, having placedgreat weight on the fact that none of theCASAC panel members expressedsupport for a standard set below 0.08ppm. In deciding between these twolevels, the Administrator took intoaccount quantitative estimates of therisks associated with attaining standardsset at these levels for those effects forwhich such quantitative risk estimatescould be developed. Other factors thatwere important in the Administrator’sproposed decision include:

(1) Quantitative estimates of 8–hourexposures of concern (i.e., at and above0.08 ppm) associated with thesestandard levels.

(2) The consistency of the clinical,field, and epidemiological studies, inwhich effects were seen not only fromcontrolled exposures to 0.08 ppm, butalso in ambient environments in which8–hour average O3 concentrationsranged from above to below the 0.08ppm level.

(3) The importance of increasedprotection for those sensitiveindividuals who may experiencerespiratory symptomatic and functionaleffects at lower O3 concentrations thanthe population as a whole.

(4) The uncertainties in consideringthe potentially more serious but as yetuncertain chronic effects.

As discussed above in Unit II.A.3.,EPA completed and made available forpublic comment supplemental exposureand risk assessments subsequent to theproposal. For any of the alternativestandards considered in the assessment,the new estimates of exposures at andabove 0.08 ppm are somewhat higherthan those available at the time ofproposal, while the new estimates ofrisks, for adverse effects includingmoderate and large decreases in lungfunction, moderate to severe respiratorysymptoms, and hospital admissions forasthmatics, are lower. However, the

relative differences in estimatedexposures and risks between alternativestandard levels remain about the sameas at the time of proposal. Thus, whilethe Administrator’s final decision takesinto account the more recentassessments, the differences in thequantitative results between the initialand supplemental assessments do notfundamentally alter the basis for thejudgments expressed at the time ofproposal.

To aid in comparing the public healthprotection associated with 8–hourstandards at the 0.08 ppm and 0.09 ppmlevels, observations from the updatedexposure and risk assessments for allnine urban areas evaluated aresummarized below (assuming the third-highest concentration form, which wasthe upper end of the range ofconsideration for forms for the 0.09 ppmlevel).

(1) The percentages of outdoorchildren exposed to O3 concentrationsat and above 0.08 ppm (at whichincreased nonspecific bronchialresponsiveness, decreased pulmonarydefense mechanisms, and indicators ofpulmonary inflammation have beenobserved in humans) while engaged inmoderate exertion are estimated to beapproximately 3 percent at the 0.08 ppmstandard level, ranging fromapproximately 2 percent to 10 percentin the nine areas, increasing toapproximately 11 percent at a standardlevel of 0.09 ppm, ranging fromapproximately 7 percent to 29 percentin the nine areas.

Updated risk estimates in terms of thepercentages14 and numbers of outdoorchildren estimated to experiencevarious health effects, and the totalnumbers of occurrences of these effectsin outdoor children, upon attainment ofthese two alternative standards for allnine urban areas combined15 are asfollows:

(2) For moderate lung function (FEV1)decreases ≥ 15 percent, approximately 6percent of outdoor children (180,000children) would experience this effectone or more times per year (650,000occurrences) at the 0.08 ppm standardlevel, increasing to approximately 8percent of outdoor children (250,000children and 1,100,000 occurrences) atthe 0.09 ppm standard level.

(3) For large lung function (FEV1)decreases ≥ 20 percent, approximately 2

percent of outdoor children (58,000children) would experience this effectone or more times per year (100,000occurrences) at the 0.08 ppm standardlevel, increasing to approximately 3percent of outdoor children (97,000children and 220,000 occurrences) atthe 0.09 ppm standard level.

(4) For moderate or severe pain ondeep inspiration, approximately 0.9percent of outdoor children (27,000children) would experience this effectone or more times per year (120,000occurrences) at the 0.08 ppm standardlevel, increasing to over 1 percent ofoutdoor children (41,000 children and220,000 occurrences) at the 0.09 ppmstandard level.

Many public commenters supportedEPA’s proposed level of 0.08 ppm for an8–hour standard, including most publichealth associations and groups ofmedical professionals, many citizens,and some States and regionalassociations. There were also largenumbers of commenters who expressedstrong views in opposition to theproposed level. Of those who did notsupport the proposed 8–hour level,almost all commenters representingbusinesses and industry associations,many local governmental groups andprivate citizens, and some States eithersupported no change to the currentstandard or, if EPA were to replace thecurrent 1–hour standard with an 8–hourstandard, supported a level of 0.09 ppmdirectly or simply one that would be‘‘equivalent’’ to the current standard. Onthe other hand, environmental groups,many citizens, and some medicalprofessionals and researchers supporteda level of 0.07 ppm for an 8–hourstandard.

In general, the issues raised by thesegroups of commenters can be addressedin three categories: Comments on thestrength and adequacy of the healtheffects evidence upon which theproposed decision was based, commentson the quantitative exposure and riskassessments and the extent to which theassessments either over- or under-predict exposures and risks amongsensitive populations, and judgments asto whether the differences in publichealth protection provided byalternative standards are significantfrom a public health perspective. Eachof these categories of key issues isdiscussed separately below.

With regard to the first category ofcomments, on the strength andadequacy of the health effects evidence,commenters who did not support theneed for any increased protectionbeyond that provided by the currentstandard questioned the adequacy orhighlighted the limitations of the


16 The initial risk assessment used both‘‘Weibull’’ and ‘‘proportional’’ air qualityadjustment procedures, whereas the supplementalrisk assessment used a ‘‘proportional’’ air qualityadjustment procedure for all nine urban areas. Inresponding to comments on the air qualityadjustment procedures, EPA also evaluated analternative ‘‘quadratic’’ procedure (as discussed inthe Response to Comments), which generallyresulted in risk estimates between those from theWeibull and proportional procedures.

various types of health effects studiesthat have related O3 exposures toadverse effects. For example, somecommenters questioned the controlledhuman exposure studies, arguing that:Many such studies used patterns ofexposures and exercise levels that arenot representative of normal populationexposures to ambient O3; some exposurechambers using artificially generated O3

may have been contaminated with otherpollutants that could have accounted forsome of the observed effects; andresponses to elevated O3 levels werecompared to responses to air withessentially no O3 rather than tobackground levels typical of ambientair. Some commenters argued that theseflaws in the study designs would resultin overestimating responses to non-background levels of ambient O3 or inerroneous findings of statisticalsignificance. In contrast, otherscommented that because the chambersdid not contain other pollutants andnatural pulmonary irritants (e.g.,pollens, dust) or a full range ofenvironmental conditions (e.g., hightemperatures and humidity) typical ofambient air, the results mayunderestimate the true impact of O3 inthe ambient air.

Some commenters also questioned thesummer camp and other field studiesand epidemiological studies reportingincreased hospital admissions andemergency room visits, arguing that:The responses in these studies wereinherently confounded by exposures toother pollutants, the camp studies didnot differentiate activity levels of theparticipants, and linear regression downto or below background levels wasunjustifiably used to analyze the resultsof the hospital admission studies. Thesecommenters expressed the view thatthese and other flaws call into questionany conclusions about whether thereported associations are causal. Incontrast, other commenters argued thatthe hospital admissions reported inthese studies are indicative of a pyramidof adverse health effects, includingincreased mortality, increased visits toemergency and outpatient departmentsand physicians, increased numbers ofasthma attacks resulting in increasedmedication use, and increased numbersof restricted activity days and acuterespiratory symptom days, that EPA hasnot adequately taken into account. TheEPA notes that these comments areconsistent with statistics published bythe U.S. Department of Health andHuman Services, which indicate that forevery hospital admission of anindividual with asthma for respiratorycauses, there are more than five

emergency and outpatient departmentvisits and more than 20 office-basedphysician visits (U.S. DHHS, 1996).

With regard to studies related topulmonary inflammation and chronicrespiratory damage, some commentersargued that the linkage betweenrepeated inflammatory responses andchronic respiratory damage was merelyspeculation, and, therefore, should notbe considered as part of the basis fordecisions on the primary standard. Incontrast, others commented that animalstudies had demonstrated that repeatedpulmonary inflammation leads todegenerative or irreversible lungdamage, that these studies are consistentwith observations in human exposurestudies, and, therefore, that they shouldbe considered in decisions on thestandard.

The EPA notes that many of thesecomments did not reflect an integrativeassessment of the evidence—theapproach CASAC has historically urgedEPA to follow—but rather a piecemeallook at each individual study or type ofstudy, which tends to miss the strengthof the entire body of evidence takentogether. Other commenters didconsider the body of evidence in a moreintegrative manner, and many of thesecommenters expressed the view that thebody of evidence as a whole providedclear evidence of O3-related effects atand below O3 concentrations allowed bythe current standard. Some commentershighlighted the large number of studiesthat demonstrate evidence of effects forprolonged exposures at and below 0.08ppm, and criticized EPA for giving toolittle weight to those studies whichreported serious effects, but for whichthe data were not sufficient to doquantitative risk assessments.

With regard to the second category ofcomments, on the exposure and riskassessments, a number of commentersraised concerns about key aspects of theassessments, including the exposuremodel, the development ofconcentration-response functions, theapplication of the risk model, and themeasures of risk used to characterize theresults of the assessments. With regardto the exposure model, a number ofcommenters claimed that: The modeloverestimates the exertion level that canbe achieved by most children andoutdoor workers and the fraction of timethat these groups spend in moderate orheavy exertion; the model overestimatesoutdoor ambient exposures becausefixed-site monitors overestimate outdoorpersonal exposures; and the air qualityadjustment procedures used to simulateattainment of the standards areinappropriate or highly uncertain. Othercommenters expressed concern that the

exposure model may be significantlyunderestimating exposures for childrenand outdoor workers who repeatedlyexercise due to limitations in theavailable human activity pattern data.

As discussed in the proposal, EPArecognizes that the exposure modelnecessarily contains many sources ofuncertainty, although every effort hasbeen made to account for suchuncertainties to the extent possible. Inparticular, the model incorporates andis sensitive to analytical proceduresused to simulate spatial and temporaldistributions of O3 concentrations thatwould occur as a result of an area justattaining any of the alternativestandards addressed in the exposureassessment. These air qualityadjustment procedures are based ongeneralized models intended to reflectthe patterns of changes in distributionsof O3 concentrations that havehistorically been observed in areasimplementing control programsdesigned to attain the O3 NAAQS. TheEPA recognizes that future changes inair quality distributions are area-specific, and will be affected bywhatever specific control strategies areimplemented in the future to attain therevised NAAQS. Thus, generalizedmodels are expected to be moreuncertain for any given area than whenexposure results are aggregated acrossmany areas (as was done across the nineurban areas analyzed in EPA’s exposureassessment).

Some commenters questioned thespecific air quality adjustmentprocedure used in the initial andsupplemental assessment16, and a few ofthese commenters recommendedrevisions or alternative procedures thatthey believed would be morerepresentative of historical or projectedfuture air quality patterns. As discussedin more detail in the Response toComments, EPA acknowledges that bothprocedures used in the assessmentsresult in projections of air quality thatdeviate to some degree from historicalpatterns of air quality changes observedin specific urban areas, and that otherprocedures may be more representativeof air quality patterns in specific areas.While EPA will take these commentsinto account as future refinements aremade to the air quality adjustment


17 The two areas are Houston and parts of LosAngeles county, which are two of only six areasnationwide with peak 1– to 8–hour design valueratios greater than 1.5.

procedures used in the exposure model,EPA believes, and CASAC concurred,that the procedures used in theassessments conducted as part of thisreview are reasonable given theuncertainties inherent in projectingfuture changes in air quality patterns.

In commenting on the air qualityadjustment procedure used in thesupplemental assessment, somecommenters particularly focused on theresults for two of the nine areasanalyzed in which, contrary to resultsfrom the initial assessment, lower riskswere estimated for the current standardas compared to the proposed standard.As discussed more fully in the Responseto Comments, EPA believes that theseresults for each area cannot bedistinguished within the sensitivity ofthe alternative air quality adjustmentprocedures used in the initial andsupplemental assessments. Further, EPAnotes that these two areas have muchhigher ratios of peak 1–hour to 8–hourO3 concentrations than the vast majorityof areas in which O3 is monitored17, andit is thus reasonable to expect thatgeneralized air quality adjustmentprocedures would be particularlyuncertain for such areas.

Comments focusing on thedevelopment of concentration- responsefunctions for use in the risk model haveincluded a number of claims. Somecommenters claimed that EPAinappropriately selected studies fordeveloping the functions by excludingstudies that reported lower responserates and by using only studiesconducted by EPA scientists. Somecommenters asserted that contaminantsin the controlled exposure chambersmay be responsible for some of theeffects incorporated into theconcentration-response functions for O3.Further, some commenters asserted thatit was inappropriate to extrapolate theconcentration-response functions tobackground levels or to developconcentration-response functions forsymptomatic responses in childrenbased on studies of such responses inadults.

Of the comments focusing on theapplication of the risk model, somecommenters claimed that the aggregaterisk results were overstated because of:Many of the methodological problemsnoted in the above summary ofcomments, the failure to take intoaccount the known attenuation ofeffects, and the assumption of aninappropriately low background

concentration in calculating risksattributable to non-background sourcesof O3. On the other hand, othercommenters claimed that aggregate riskresults were understated because of:Methodological problems, noted above,that underestimate exposures, limitingthe analyses to only a subset of adversehealth effects rather than estimating thefull range of effects that have beenattributed to O3, and by focusing onlyon nine urban areas rather thanprojecting risk reductions fromalternative standards nationally.

While EPA has includedcomprehensive responses to thesecomments in the Response toComments, most of the issues andconcerns raised by commentersconcerning the health effects evidenceand the methods used in the exposureand risk assessments are essentiallyrestatements of concerns raised duringthe review of the Criteria Document andthe development and review of thesequantitative assessments as part of thepreparation and review of the StaffPaper. EPA presented and the CASACreviewed in detail the approaches usedto assess exposure and health risk, thestudies and health effect categoriesselected for which concentration-response functions were estimated, andthe presentation of the exposure andrisk results summarized in the StaffPaper. As stated in the proposal, EPAbelieves and CASAC concurred, that thegeneral models selected to estimateexposure and risk are appropriate andthat the methods used to conduct theexposure and risk assessments representthe state of the art. EPA does not believethat the exposure or risk assessments arefundamentally biased in one directionor the other as claimed in some of thecomments.

The Administrator and CASAC haverecognized, however, that there aremany uncertainties inherent in suchassessments and that the resultingranges of quantitative risk estimates donot reflect all of the uncertaintiesassociated with the numerousassumptions inherent in such analyses(Wolff, 1995b). EPA summarized someof the most important caveats andlimitations concerning both theexposure analyses and the riskassessments for lung function changes,respiratory symptoms, and hospitaladmissions in the proposal. A morecomplete discussion of assumptions anduncertainties is contained in the StaffPaper and technical support documents(Johnson et al., 1996 a,b; Whitfield et al.,1996; Richmond, 1997).

With regard to the third category ofcomments, reflecting commenters’judgments as to whether the differences

in public health protection of alternativestandards are significant from a publichealth perspective, EPA notes thathighly divergent judgments wereexpressed by different groups ofcommenters. A large number ofcommenters who expressed the viewthat the differences in public healthprotection were not significant orimportant enough to warrant anystandard more stringent than the currentstandard used CASAC as the basis fortheir position, as discussed above inUnit II.B.1. on averaging time. Otherscited small percentages of outdoorchildren and other sensitive groupslikely to be affected based on EPA’sassessment, or even smaller percentagesas modified by analyses conducted bythe commenter to correct perceivederrors in the analyses. In contrast, othercommenters cited large total numbers ofchildren likely to be affected, not onlyfor the subset of O3-related effects andthe nine areas analyzed in EPA’sassessments, but also for a broader arrayof related effects projected nationally.

The core issue in this review of theprimary O3 standard, as stated by theAdministrator at the time of proposal, iswho is to be protected, and from what.Clearly, for pollutants, such as O3, thathave no discernible thresholds forhealth effects, no standard can be risk-free. The Administrator’s task is toselect a standard level that will reducerisks sufficiently to protect publichealth with an adequate margin of safetysince a zero-risk standard is neitherpossible nor required by the Act. AsCASAC and the Administratorrecognize, the selection of a specificstandard level for such pollutantsrequires public health policy judgmentsin addition to determinations of astrictly scientific nature.

In making such judgments, theAdministrator rejects the notion thatbecause standards cannot be risk-freethey should not be revised to provideincreased protection for sensitivepopulations, particularly includingchildren in this case, when availableevidence points to greater impacts onpublic health than had previously beendemonstrated. In carefully reassessingboth those risks to public health thatcan be quantified as well as those forwhich quantitative risk information ismore limited, the Administrator hasfocused on the following comparisonsbetween the degree of public healthprotection likely to be afforded by an 8–hour standard at the proposed level of0.08 ppm and an alternative standardset at a level of 0.09 ppm (assuming thesame third-highest concentration form):

(1) Based on EPA’s updated analysesof estimated moderate or large decreases


18 The EPA anticipates that additional peoplewould be protected through regional measuresadopted for purposes of an 8–hour, 0.08 ppmstandard.

19 The term ‘‘expected’’ means that the numbersof exceedances per year are averaged over 3 yearsand may be calculated using specific adjustmentsto account for missing data.

20 The 1-expected-exceedance form essentiallyrequires the fourth-highest air quality value in 3years, based on adjustments for missing data, to beless than or equal to the level of the standard forthe standard to be met at an air quality monitoringsite.

in lung function and moderate to severepain on deep inspiration in outdoorchildren in nine urban areas (Richmond,1997), a standard set at 0.09 ppm wouldallow approximately 40 percent to 65percent more outdoor children toexperience such effects than would a0.08 ppm standard, and approximately70 percent to 120 percent moreoccurrences of such effects in outdoorchildren per year.

(2) While only relatively smallpercentages of outdoor children areestimated to experience such effects, thedifferences in these percentagesbetween the two standard levelsrepresent tens of thousands morechildren, and hundreds of thousandsmore occurrences of adverse effects inthese children, in these nine urban areasalone, for a 0.09 ppm standard ascompared to a 0.08 ppm standard.

(3) Based on EPA’s updated riskassessment of increased hospitaladmissions in New York City(Richmond, 1997), a standard set at 0.09ppm would allow approximately 40more excess hospital admissions ofasthmatics within an O3 season in NewYork City for respiratory causes ascompared to a 0.08 ppm standard,which represents approximately a 40percent increase in excess O3-relatedadmissions, but only approximately a0.3 percent increase in total admissionsof asthmatics. The EPA believes thatwhile these numbers of hospitaladmissions are relatively small from apublic health perspective, they areindicative of a pyramid of much largernumbers of related O3-induced effects,including respiratory-related hospitaladmissions among the generalpopulation, emergency and outpatientdepartment visits, doctors visits, andasthma attacks and related increased useof medication that are important publichealth considerations.

(4) Based on EPA’s exposure analysesin the nine urban areas, a standard setat 0.09 ppm would allow more thanthree times as many children toexperience 8–hour average exposures ofconcern as would a 0.08 ppm standard,with the number of outdoor childrenlikely to experience such exposuresincreasing from approximately 100,000to more than 300,000 in the nine urbanareas alone, representing an increasefrom approximately 3 percent toapproximately 11 percent of the outdoorchildren likely to experience suchexposures.

(5) These exposures of concern arejudged by EPA to be an importantindicator of the public health impacts ofthose O3-related effects for whichinformation is too limited to developquantitative estimates of risk, but which

have been observed in humans at a levelof 0.08 ppm for 6– to 8–hour exposures.Such effects include the following:increased nonspecific bronchialresponsiveness (related, for example, toaggravation of asthma), decreasedpulmonary defense mechanisms(suggestive of increased susceptibility torespiratory infection), and indicators ofpulmonary inflammation (related topotential aggravation of chronicbronchitis or long-term damage to thelungs).

(6) To put these risks and exposuresinto broader perspective, EPA notes thatapproximately 46 million more people,including approximately 13 millionmore children and 3 million moreindividuals with asthma, live in areasthat would not attain a 0.08 ppmstandard compared to a 0.09 ppmstandard. The general population aswell as children and asthmatics wouldbreathe cleaner air as a direct result ofcontrol measures designed to bring areasinto attainment with the proposedstandard.18

While recognizing the inherentuncertainties in these estimates, andafter taking into account the range ofviews and judgments expressed in thepublic comments, the Administratorfinds the public health impactsdescribed in the proposal, as updatedabove, to be important and sufficientlylarge as to warrant a standard set at alevel of 0.08 ppm, as proposed.

The Administrator recognizes theviews of those who argue that similarlylarge improvements in public healthprotection would result from a standardset at 0.07 ppm as compared to theproposed standard, such that, based onthe same reasoning, the evidencewarrants a standard set at 0.07 ppm. Inconsidering these views, theAdministrator gives significant weightto the following considerations:

(1) No member of the CASAC panel ofexperts supported a standard set lowerthan 0.08 ppm, specifically afterconsidering a range of alternativestandards that included 0.07 ppm.

(2) The most certain O3-related effects,while judged to be adverse, are transientand reversible (particularly at O3

exposures below 0.08 ppm), and themore serious effects with greaterimmediate and potential long-termimpacts on health are less certain, bothas to the percentage of individualsexposed to various concentrations whoare likely to experience such effects andas to the long-term medical significanceof these effects.

(3) As many commenters have noted,based on information in the CriteriaDocument with regard to ambientconcentrations of O3 from backgroundsources, an 8–hour standard set at a 0.07ppm level would be closer to peakbackground levels that infrequentlyoccur in some areas due tononanthropogenic sources of O3

precursors, and thus more likely to beinappropriately targeted in some areason such sources.

After taking into account the publiccomments, and for the reasons outlinedabove, the Administrator finds that astandard set at a level of 0.07 ppm is notrequisite to protect public health withan adequate margin of safety.

3. Form. The form of the current 1–hour, 0.12 ppm standard is a ‘‘1-expected-exceedance’’ form. That is, thecurrent standard is based on theexpected19 number of days per year, onaverage over 3 years, on which the levelof the standard is exceeded, and limitsthat number of expected exceedances tobe less than or equal to 1.0.

In evaluating alternative forms for theprimary standard, the adequacy of thepublic health protection provided wasthe Administrator’s foremostconsideration. The Administrator alsorecognized, however, that concerns havebeen raised with the current form sinceit was promulgated in 1979 due to theinherent lack of year-to-year stability inthe measure of air quality on which the1-expected-exceedance form is based.20

The CASAC specifically took suchconcerns into account in recommendingthat the current form be revised and innoting that a more robust,concentration-based form wouldminimize such instability and providesome insulation from the impacts ofextreme meteorological events that areconducive to O3 formation (Wolff,1995b). Such instability can have theeffect of reducing public healthprotection by disrupting ongoingimplementation plans and associatedcontrol programs.

As discussed in the proposal, basedon information presented in sections IV.and V.I of the Staff Paper and the adviceof CASAC, the Administrator focusedher consideration on the followingalternatives:

(1) Revising the current 1-expected-exceedance form of the standard to


21 Areas that ‘‘just attain the standard’’ aredefined as those whose design value falls between0.075 and 0.084 ppm.

22 Peak 8–hour average concentrations are definedin terms of the fourth-highest daily maximumconcentration in 3 years (i.e., the design value forthe current 1-expected-exceedance form of thestandard).

23 The results of these air quality analyses arepresented in Freas (1996) and summarized in theproposal for the third- and fifth-highestconcentration forms and the 3– and 5-expected-exceedance forms. Based on these considerations,and the air quality comparisons in particular, theAdministrator judged that the middle of the rangeof exceedances considered, three expectedexceedances, or the comparable third-highestconcentration, represented a reasonable policychoice, and proposed the 3–year average of theannual third-highest daily maximum 8–houraverage O3 concentrations as the form of thestandard. In recognition of a range of views on thedegree of health protection that would beappropriate, she also solicited comment on otherconcentration-based forms, including the second-,fourth-, and fifth-highest concentration forms.

allow for multiple (up to five) expectedexceedances per year, averaged over 3years. A multiple-exceedance formwould be based on a less extreme airquality statistic and, thus, wouldincrease the stability of the expected-exceedance form.

(2) Adopting a concentration-basedstatistic, such as the 3–year average ofthe nth-highest daily maximum 8–houraverage O3 concentration, as analternative to an expected exceedancestatistic. Air quality analyses presentedin the Staff Paper indicate that the 3–year averages of the annual third-,fourth-, and fifth-highest dailymaximum 8–hour concentrations wouldprovide approximately the same healthprotection as the 3-, 4-, and 5-expected-exceedance forms averaged over thesame period, respectively.

It was the consensus of the CASACPanel that this range of allowableexceedances (i.e., up to 5 exceedances),and the consideration of comparableconcentration-based forms, wasappropriate. Further, CASACacknowledged that selecting fromwithin this range of alternative forms isa policy judgment, especially given thenature of the health effects and theabsence of a ‘‘bright line’’ that clearlydifferentiates between acceptable andunacceptable risks within this range. All10 CASAC Panel members whoexpressed specific opinions on the formof the standard favored one that wouldallow for multiple exceedances (Wolff,1995b).

In reaching her proposed decision onthe form of an 8–hour standard set at0.08 ppm, the Administrator had tochoose a specific form within the rangeof up to 5 allowable exceedances or upto the comparable fifth-highestconcentration, and either anexceedance-based or a concentration-based form. As discussed in theproposal, in considering possible formswithin the range of 1 to 5 exceedances(or their concentration-basedcounterparts) the Administrator tookinto consideration aggregate riskestimates for those health effects forwhich quantitative risk analyses havebeen done; estimated exposuresassociated with those effects for whichno quantitative risk estimates could bedeveloped; and the magnitude of peakmeasurements of 8–hour average O3

concentrations, and the number of dayson which the level of the standardwould likely be exceeded, based on ananalysis of historical air quality data(Freas, 1996). In considering exposureand risk estimates available at the timeof proposal for 1– and 5-expected-exceedance forms, the Administratornoted that the level of the standard is a

more dominant factor in determiningthe degree of exposure and riskreductions achieved, with the formbeing associated with smallerdifferences in risk estimates within acontinuum of risk. In considering airquality comparisons for standardsacross the range of forms considered,the Administrator focused in particularon the extent to which alternative formswould limit the number of days inwhich the level of the standard wouldbe exceeded in areas that just attain thestandard21, and the magnitude of peak8–hour average O3 concentrations22 thatwould occur in such areas.23 Morespecifically, the Administrator took intoconsideration the percentage ofmonitoring sites just attaining an 8–hour, 0.08 ppm standard that wouldhave 8–hour peak O3 concentrationsabove a benchmark level of 0.09 ppm.This benchmark level is the upper endof the range of levels endorsed byCASAC for an 8–hour O3 standard. TheAdministrator believes, given theuncertainties associated with this kindof complex health decision, that it is anappropriate goal to limit the percentagesof areas experiencing such daily peaks.

In choosing to propose aconcentration-based form, theAdministrator recognized theadvantages of a concentration-basedform over an exceedance-based form. Asdiscussed in the proposal, the principaladvantage of a concentration-based formis that it is more directly related to theambient O3 concentrations that areassociated with health effects. That is,given that there is a continuum ofeffects associated with exposures tovarying levels of O3, the extent to whichpublic health is affected by exposure toambient O3 is related to the actualmagnitude of the O3 concentration, notjust whether the concentration is above

a specified level. With an exceedance-based form, days on which the ambientO3 concentration is well above the levelof the standard are given equal weightto those days on which the O3

concentration is just above the standard(i.e., each day is counted as 1exceedance), even though the publichealth impact on the two days issignificantly different. With aconcentration-based form, days onwhich higher O3 concentrations occurwould weigh proportionally more thandays with lower O3 concentrations,since the actual concentrations are useddirectly in determining whether thestandard is attained. A concentration-based form also has greater temporalstability than the expected-exceedanceform and, thus, would facilitate thedevelopment of more stableimplementation programs by the States.

As discussed above in Units II.A.3.and II.B.2., EPA completed and madeavailable for public commentsupplemental exposure and riskassessments subsequent to the proposal.These updated assessments, whichspecifically analyzed the third- andfifth-highest concentration-based forms,aid in comparing the differences inpublic health protection amongalternative concentration-based formswithin the range considered in theproposal for 8–hour, 0.08 ppmstandards. Based on these updatedassessments, the Administrator againnotes that the level of the standard is themore dominant factor in determiningthe degree of risk reduction achieved,with these alternative forms beingassociated with much smallerdifferences in risk estimates within acontinuum of risk. For example, withinthe nine urban areas included in the riskassessment, approximately 180,000outdoor children would experiencemoderate lung function (FEV1)decreases ≥ 15 percent upon attainmentof an 8–hour, 0.08 ppm standard witha third-highest concentration form,compared to approximately 200,000outdoor children with a fourth-highestconcentration form and 220,000 outdoorchildren with a fifth-highestconcentration form.

The public comments include a largenumber that specifically addressed theform of the standard. Those commenterswho expressed views on the form of thestandard can be divided into threegroups, according to the level of 8–hourstandard and the relative degree ofpublic health protection that thecommenter supported. These groupsinclude: Commenters who supported an8–hour, 0.08 ppm standard to provideincreased public health protectionrelative to the current standard;


commenters who supported either an 8–hour, 0.09 ppm standard, or simply an8–hour standard ‘‘equivalent’’ to thecurrent standard; and commenters whosupported an 8–hour, 0.07 ppmstandard to provide a greater margin ofsafety than that afforded by theproposed standard.

The first group included many privatecitizens, some medical professionalsand researchers, and some States andlocal governmental groups. While anumber of commenters in the first groupspecifically supported the proposedthird-highest concentration form,generally for the reasons presented inthe proposal, others supported either a1-expected-exceedance form or aconcentration-based form in the upperpart of the range (i.e., the fourth- orfifth-highest forms). The second groupof commenters, which included manylocal governmental groups and privatecitizens, some States, and mostcommenters representing businessesand industry associations, almostexclusively supported a concentration-based form in general, and a form in theupper part of the range (or above therange) in particular. In sharp contrast,the third group of commenters, whichincluded environmental groups, manyprivate citizens, and some medicalprofessionals and researchers, almostexclusively supported a 1-expected-exceedance form in conjunction with an8–hour, 0.07 ppm standard to providethe largest margin of safety within therange of alternative standardsconsidered.

To the extent that the second andthird groups of commenters argued fora different level than the Agency adoptstoday, the Administrator disagrees withtheir comments for the reasons set forthin the discussion of the standard levelabove in Unit II.B.2. To the extent thatthey argued for more than 5exceedances (or the concentration-basedequivalent), the Administrator disagreeswith their views because such forms falloutside the range recommended byCASAC and would provide less publichealth protection than she deemsappropriate. To the extent that thesecond and third groups of commentersaddressed the merits of particular formswithin the range of forms considered inthe proposal, they raised points similarto those raised by commenters in thefirst group. These points are discussedbelow.

Among the commenters in the firstgroup (i.e., those supporting an 8–hour,0.08 ppm standard to provide increasedpublic health protection), many felt thatthere was no compelling basis forselecting the third-highest rather thanthe fourth- or fifth-highest

concentration-based form. Thesecommenters frequently quoted CASAC’sclosure letter (Wolff, 1995b) as stating‘‘that there is no bright line’ whichdistinguishes any of the proposedstandards (either the level or thenumber of exceedances) as beingsignificantly more protective of publichealth,’’ and that ‘‘the selection of aspecific level and number of allowableexceedances is a policy judgment.’’ Ingeneral, these commenters did not giveweight to the air quality comparisonsthat were a major consideration in theAdministrator’s decision to propose thethird-highest concentration form. Somecommenters seem to view such airquality comparisons, particularly withregard to pollutants such as O3 that haveno discernible threshold of effects, asrelating more to people’s perceptions ofhow well air pollution is controlledthan to any objective measure of actualrisks to public health.

These commenters made a number ofpoints in questioning the need tospecify an 8–hour, 0.08 ppm standard interms of the third-highest rather thanthe fourth- or fifth-highest concentrationform. Many noted that a change to an 8–hour averaging time in and of itselfwould appropriately focus air qualitymanagement programs on prolongedexposures of most concern. Further,many noted that a level of 0.08 ppm,regardless of the form within the rangeof forms considered in the proposal,would provide significantly increasedprotection from O3-related risks topublic health associated with acuteeffects (i.e., those resulting from short-term and prolonged exposures) forwhich they believe there is sufficientevidence to be used as a basis for astandard at this time. Some of thesecommenters expressed the view that thepotential for chronic effects (i.e., thoseresulting from long-term exposures)would be better addressed throughcontinued research, rather than byadding a greater margin of safety to arevised standard based primarily oneffects of short-term and prolongedexposures. Many of these commentersrecognized, as did EPA in the proposal,that there is a continuum of risksassociated with O3 exposures, that nostandard can therefore be risk-free, andthat there are large uncertainties in anyestimates of the degree of protectionassociated with alternative forms. Ingeneral, these commenters also notedthat, for the same reasons, CASACadvised that the selection of a form fromwithin the range considered in theproposal was a policy judgment, not onethat could be decided on the basis ofscience alone. In essence, these

commenters argued that a morerestrictive form than the upper part ofthe range endorsed by CASAC is notrequisite to protect public health.

In contrast, other commenters in thefirst group (i.e., those supporting an 8–hour, 0.08 ppm standard) supportedeither the proposed third-highest orsecond-highest concentration form or a1-expected-exceedance form. Thesecommenters generally gave greaterweight to limiting the magnitude ofpeak O3 concentrations and the numberof days on which the standard levelwould be exceeded in areas meetingsuch a standard, and, in some cases, toproviding a greater margin of safety toaccount for potential chronic effects.Such views suggest that limiting thenumber of days on which the standardlevel would be exceeded, for example,is an important factor in riskcommunication and in the public’sunderstanding of the degree to which astandard protects people from exposuresto O3 that may interfere with theirability to engage in normal activities ormay result in the need for increasedmedication or medical treatment,especially for those individuals withasthma or other respiratory diseases. Asdiscussed above in this unit, althoughsome of these commenters felt that thethird-highest concentration form wouldprotect public health while alsoproviding increased stability, othersexpressed concern that public healthcould be compromised by any form thatallowed for multiple exceedances of thestandard. The advantages of forms thatallow for multiple exceedances, thusproviding increased stability asdiscussed in the proposal, and the viewsof the CASAC panel members whoexpressed opinions, all of whom favoredsuch forms, were not given weight bycommenters within this group whosupported a 1-expected-exceedanceform.

The Administrator has carefullyreassessed the relative risks to publichealth of specific forms within the rangeof the second- to fifth-highestconcentration forms or theirexceedance-based equivalents, takinginto account the public commentssummarized above, and the advice fromCASAC Panel members that the currentform be replaced by a form that allowsmultiple exceedances. In doing so, theAdministrator focused on the followingconsiderations:

(1) The CASAC advised thatconcentration-based forms, within therange considered up to the fifth-highestconcentration form, are appropriate fora health-based primary O3 standard, andthat selection from within this range isa policy judgment that cannot be based


on science alone. This advice reflectsCASAC’s recognition that O3 exhibits acontinuum of effects, such that there isno discernible threshold above whichpublic health protection requires that noexposures be allowed or below whichall risks to public health can be avoided.The CASAC also recognized that aconcentration-based form wouldincrease the stability of the standard byproviding some insulation from theimpacts of extreme meteorologicalevents (Wolff, 1995b).

(2) Estimates of the differences in riskto public health, for those effects thatcould be considered quantitatively,within a range of alternative forms fromthe second- to fifth-highestconcentrations (for an 8–hour, 0.08 ppmstandard) are relatively small comparedto the differences between alternativelevels. In other words, the choice oflevel is substantially more important tothe degree of public health protectionafforded by the standard than the choiceof form from within this range of forms.

(3) Measures that distinguish betweenthe alternatives within the range of thesecond- to fifth-highest forms, based onair quality analyses, reflectconsiderations related to how someindividuals understand the degree towhich an air quality standard protectspublic health. These considerations area distinct aspect of risk communicationto individual citizens even though thedays on which exceedances occur areaccounted for in EPA’s quantitativeassessments of risks to public health.

(4) To assess the comparative effect ofall forms within the range of the second-to fifth-highest concentration forms,EPA considered air quality comparisonsfor all such forms (Freas, 1996). Thesecomparisons (based on 1993 to 1995data) show that 8–hour, 0.08 ppmsecond- and third-highest concentrationstandards are very similar in that eachstandard limits the percent ofmonitoring sites that would experiencepeak days above the benchmark level of0.09 ppm to 1 percent of such sites, andthe number of days on which thestandards would likely be exceeded inthe worst of 3 years would be no morethan 6 and 7, respectively. While lessrestrictive than either of thesestandards, an 8–hour, 0.08 ppm fourth-highest concentration standard wouldbe significantly more restrictive than afifth-highest standard. For example, the8–hour, 0.08 ppm fourth-highestconcentration standard would limit thepercent of monitoring sites that wouldexperience peak days about thebenchmark level of 0.09 ppm to 8percent of such sites, and the number ofdays on which the standards wouldlikely be exceeded in the worst of 3

years would be no more than nine. Incomparison, the fifth-highestconcentration standard would limit thepercent of monitoring sites that wouldexperience peak days about thebenchmark level of 0.09 ppm to 17percent of such sites, and the number ofdays on which the standards wouldlikely be exceeded in the worst of 3years would be no more than 11.

(5) The extent to which thealternatives within the range of thesecond- to fifth-highest concentrationforms provide protection against themore serious, but less certain effects thathave been associated with exposure toO3, including potential chronic effects,cannot be quantitatively assessed at thistime. Given that all such forms wouldresult in significant reductions inexposures to O3 at and above 0.08 ppm(the level where suggestive evidence ofsuch effects is available), any formwithin this range would provide somemargin of safety against these effects.

Based on these considerations, theavailable health effects evidence, thequantitative assessments contained inthe Criteria Document, Staff Paper, andsupplemental analyses and supportingdocuments, and the range of views andjudgments expressed in the publiccomments on the appropriate form, theAdministrator has reconsidered theform of the standard that is requisite toprotect public health with an adequatemargin of safety. As an initial matter,the Administrator has decided to adopta concentration-based form whichallows for more than one exceedance.While the Adminstrator understands theviews of the many citizens who areconcerned about a standard that wouldallow for multiple days on which thelevel of the standard may be exceeded,the Administrator concludes that suchconcerns are more relevant forpollutants that exhibit a clear thresholdof effects than for pollutants such as O3

that exhibit a continuum of effects. TheAdministrator believes that the publichealth risks associated with suchpollutants can be appropriatelyaddressed through a standard thatallows for multiple exceedances toprovide increased stability, but that alsosignificantly limits both the number ofdays on which the level may beexceeded and the magnitude of suchexceedances. This approach recognizesthat exposures associated with suchexceedances are already reflected in theexposure and risk assessments that werean important consideration in selectinga 0.08 ppm level for the primary O3

standard, and that increased stability inthe standard is important to avoiddisruption to ongoing control programs,

and thus to maintain ongoing publichealth protection.

Having again concluded that aconcentration-based O3 standard thatallows for multiple exceedances isappropriate, the Administratorconsidered the extent to which the formof an 8–hour standard should beselected so as to provide a margin ofsafety against possible, but uncertainchronic effects. The Administratorcarefully considered the views of themany commenters who emphasized theuncertainties in the evidence, primarilyfrom laboratory animal studies, that wasavailable in this review of the criteriaand standards to relate long-termexposures to ambient levels of O3 topossible chronic effects in humans.These commenters, as did CASAC,advised that further research intopotential chronic effects in humansshould be continued, and the resultsconsidered in the next review of the O3

standard. The Administrator ispersuaded that the difference betweenthe margins of safety for these potentialchronic effects afforded by thealternatives within the range of thesecond- to fifth-highest concentrationforms is not well enough understood atthis time to use as the basis for choosingthe most restrictive forms (i.e., thesecond- or third-highest concentrationform). On the other hand, theAdministrator also judges that therelatively large percentage of sites thatwould experience O3 peaks above abenchmark level of 0.09 ppm even whenattaining a fifth-highest concentrationstandard and the number of days onwhich the level of a fifth-highestconcentration standard may beexceeded argue against choosing thatform, which is the least restrictivewithin the range considered.

For the reasons outlined above, andtaking into account the range of viewsin the public comments, theAdministrator concludes that anintermediate form, the fourth-highestconcentration form, would serve toappropriately balance these publichealth considerations in conjunctionwith the 8–hour averaging time and 0.08ppm level selected, as discussed abovein Units II.B.1. and II.B.2., that are ofprimary importance in determining thedegree of public health protectionafforded by the standard. In addition,the Administrator notes that based onan analysis of air quality in countiesthat would attain an 8–hour, 0.08 ppmfourth-highest concentration standard(based on 1993–1995 data), over 99percent of such counties would beexpected to have four or fewer days onwhich the level of the standard isexceeded in an average year (Freas,


1997). This number of exceedances isclearly within the range of multipleexceedances that CASAC judged to beappropriate for a health-based primaryO3 standard. Thus, in theAdministrator’s judgment, based on theinformation currently available, an 8–hour, 0.08 ppm standard with a fourth-highest concentration form will protectpublic health with an adequate marginof safety.

In the proposal, which maintained thecurrent approach of using air qualitydata from the monitor measuring thehighest O3 concentrations in an area todetermine whether the primary standardfor O3 is attained, the Administratorsolicited comment on the alternative ofusing some form of averaging acrossmonitors. As discussed in the proposal,EPA recognized that during the reviewof the Staff Paper, a number ofcommenters suggested that averagingacross monitors might be appropriate toincrease the degree to which monitoringdata used in determining attainment ofthe standard reflects populationexposure and aggregate populationhealth risk. Further, these commenterssuggested that averaging data frommultiple monitors in an area wouldproduce a more stable measure of airquality and would take into accountbroader population exposure patternsacross an area than would the currentapproach of considering data from eachmonitor independently.

The Administrator did not proposethe use of spatial averaging because ofconcerns outlined in the proposalincluding: The difficulty in determiningan appropriate level for a spatiallyaveraged primary standard given thatthe bulk of the human health effectsevidence supporting a decision on anappropriate O3 standard is based oncontrolled human exposure studies thatrelate known O3 exposures directly toresponses in individuals; and questionsas to whether adequate healthprotection would be provided toindividuals within the populations thatlive or work in communities thatroutinely experience higher O3

concentrations within a broadmetropolitan area.

To address these two concerns, itwould be necessary to define criteria forgeographic locations or communities(e.g., spatial averaging zones) withinwhich the use of spatially averaged O3

data would be acceptable. Such criteriawould be important since O3 air qualityconcentrations can vary significantlyacross most urban areas. The lowestconcentrations typically occur in theurban center and in locations near O3

precursor sources, mid-rangeconcentrations in neighborhoods and

locations surrounding the urban center,and peak concentrations are typicallymeasured downwind along theoutermost suburban regions of the urbanarea. Also, the location of residences,schools, parks, and other places whereindividuals might be exposed morefrequently to ambient O3 concentrationsof concern would be an importantconsideration. Unless the O3

concentration gradients within eachspatial averaging zone were relativelyhomogeneous, there may be significantnumbers of sensitive individualsexposed to high O3 concentrations inareas where the spatial average indicatesthat the overall air quality is acceptable.

In the proposal, EPA also noted theneed to help State and localgovernments devise different O3

monitoring networks by revisingrelevant regulations and guidance,should spatial averaging be adopted.This would likely involve defininggeneral criteria for monitoring networkdesign, siting, and spatial averagingzones in nationally implementableterms, with case-by-case evaluation ofeach monitoring network. The EPArecognized that this activity wouldplace additional burdens on State andlocal air quality management districts.

In soliciting comment on whether itwould be desirable to adopt some formof spatial air quality averaging for O3,

the Administrator also solicitedcomment on specific alternativeapproaches that could be used toaddress the issues of concern. Inparticular, the Administrator wasinterested in analyses that informquestions about monitoring networkdesign, siting requirements, andapproaches for specification of spatialaveraging zones; the distribution ofpublic health protection that wouldresult from such alternative approaches;and the extent to which the level of thestandard would need to be adjusted, ifany, to provide public health protectionconsistent with the level of protectioncontemplated in the proposal.

The EPA received many comments onthe subject of using spatially averageddata to determine when the primarystandard for O3 is attained. Commentersfrom business and industry associationsfrequently supported the use of spatiallyaveraged data, as did many localgovernments and a small number ofStates, principally because it wouldprovide a more stable air qualityindicator and would better representpopulation exposure and risk. Some ofthese commenters felt that the use ofspatial averaging would be consistentwith the use of risk assessment as apolicy tool for standard setting. Many ofthese commenters agreed that the

heterogeneity of O3 concentrationsacross geographic areas would need tobe addressed by network design, with afew expressing the opinion that thiswould not be an insurmountableproblem given that there is continualmovement of monitors within existingnetworks. Some commenters suggestedaveraging approaches that included theuse of population weighting ofmonitored data, and some supported theuse of a public health informationsystem to allow individuals residing in‘‘hot spot’’ areas to reduce theirexposures to O3 concentrations ofconcern.

In contrast, environmentalassociations, public healthprofessionals, most States, and manyindividuals voiced strong concerns thatthe use of spatially averaged data wouldroutinely allow individuals who live orwork in communities with consistentlyhigher O3 levels than those occurringacross the broader urban area to beexposed to concentrations of concern.Many of these commenters raised theissue of environmental equity,expressing the view that communitieswith consistently higher O3

concentrations typically are composedpredominantly of individuals of lowersocioeconomic status, or are composedof a predominantly minority population.The EPA notes that this view is notconsistent with the air quality datadiscussed earlier in this unit, in that O3

concentrations are typically lower inurban centers than in locationssurrounding or downwind of urbancenters. Some commenters also raisedconcerns about the complexity andburdens associated with redesigningexisting monitoring networks.

Taking into account the commentsreceived, the Administrator does notfind that the issues of concern, asoutlined in the proposal and above,have been adequately addressed in thisreview of the O3 standard. In particular,while EPA strongly agrees with theimportance of public health advisoriesin addition to adequately protectivestandards, relying on the use of publichealth advisories to provide informationfor at-risk populations who mayconsistently be exposed to localized O3

concentrations of concern is consideredby the Administrator to be aninsufficient approach to protectingpublic health with an adequate marginof safety. Further, the suggested use ofpopulation weighting of monitored datamay, in many cases, be insufficientlysensitive to local O3 variations to ensureadequate protection of thesepopulations from localized O3

concentrations. Thus, the revised O3

standard will maintain the current


24 For a discussion of these programs, see theproposal.

25 Currently, a PSI value of 100 for O3

corresponds to an ambient concentration of 0.12ppm, averaged over 1 hour.

approach of using air quality data fromthe monitor measuring the highest O3

concentrations in an area to determinewhether the standard is attained withinan area.

The EPA has also considered spatialaveraging in the context of the decisionto revise the PM NAAQS, in part, byadopting a form of an annual standardfor fine particles (i.e., PM2.5) that allowsfor spatial averaging within appropriatecriteria. It is important to note thatdifferent considerations apply in thesetwo cases. One principal difference isthe nature of the health effects evidencefor O3 and PM2.5. When consideringaveraging approaches for O3, it shouldbe recognized that much of the humanhealth effects evidence supporting theO3 standard is based on controlledhuman exposure studies that relateindividual O3 exposures directly toresponses in individuals, whereas thehealth effects evidence supporting thePM2.5 standards is from epidemiologicalstudies relating community measures ofPM2.5 concentrations to population-wide responses. Thus, informationavailable for determining an appropriatelevel of a standard in these two cases ispredominantly individual-oriented inthe case of O3 and community-orientedin the case of PM2.5. As a consequence,additional research and exposure andrisk assessments beyond those availablein this review would be necessary toprovide a basis for further considerationof a spatially averaged standard for O3.The EPA will continue to explore thisapproach.

Another important difference betweenthe O3 and PM standards is that thesuite of annual and 24–hour PM2.5

standards permits the use of the 24–hour PM2.5 standard, which would notbe spatially averaged, as a backstop tocontrol localized ‘‘hot spots,’’ whereas asingle O3 standard does not allow forsuch a dual approach. Also, EPA notesthat the existence of an established,extensive O3 monitoring network wouldrequire substantial redesigning andrelocation of monitors for the purpose ofspatial averaging, in contrast to thecurrent absence of such a network forPM2.5 which can be newly designed toaddress community-oriented monitoringfrom the outset.

As discussed in the proposal, theAdministrator recognizes that nostandard within the range of levels andforms considered in this review,including the selected standard, is riskfree, due to the continuum of risk likelyposed by exposures to ambient O3

potentially down to background levels.Accordingly, consistent with CASACadvice, the Administrator solicitedcomment in the proposal on elements of

an enhanced public health advisorysystem. The Administrator believes thatthe information that could be madeavailable through such a public healthadvisory system would be particularlyuseful to extremely sensitiveindividuals in making personaldecisions about avoiding exposureswith the potential to cause transientadverse effects on days when 8–houraverage O3 concentrations are predictedto be at or near the level of the standard.Approaches to developing an enhancedsystem, and comments received on suchapproaches, are discussed in Unit II.C.of this preamble.

4. Final decision on the primarystandard. After carefully consideringthe information presented in the CriteriaDocument and the Staff Paper, theadvice and recommendations ofCASAC, public comments received onthe proposal, and for the reasonsdiscussed above, the Administrator isreplacing the existing 1–hour, 0.12 ppmprimary standard with a new 8–hour,0.08 ppm primary standard. The new 8–hour standard will become effectiveSeptember 16, 1997.

The 8–hour, 0.08 ppm primarystandard will be met at an ambient airquality monitoring site when the 3–yearaverage of the annual fourth-highestdaily maximum 8–hour average O3

concentration is less than or equal to0.08 ppm. Data handling conventionsare specified in a new Appendix I to 40CFR part 50 as discussed in Unit VIbelow.

In the proposal, EPA proposed thatthe revocation of the existing 1–hour O3

standard be delayed for certain purposesuntil EPA had approved StateImplementation Plans to implement thenew 8–hour O3 standard. EPA hadproposed continuing the applicability ofthe 1-hour standard in this way in orderto facilitate continuity in public healthprotection during the transition to a newstandard. (See Memorandum from JohnS. Seitz to Mary D. Nichols, November20, 1996; Docket No. A–95–58, item II–B–3.) Also, at the time of the proposalof the new O3 standard, EPA hadproposed an interpretation of the Act inthe proposed Interim ImplementationPolicy (61 FR 65764, December 13,1996) under which the provisions ofsubpart 2 of part D of Title I of the Actwould not apply to existing O3

nonattainment areas once a new O3

standard becomes effective.In light of comments received

regarding the interpretation proposed inthe Interim Implementation Policy, EPAhas reconsidered that interpretation andnow believes that the Act should beinterpreted such that the provisions ofsubpart 2 continue to apply to O3

nonattainment areas for purposes ofachieving attainment of the current 1–hour standard. As a consequence, theprovisions of subpart 2, which governimplementation of the 1–hour O3

standard in O3 nonattainment areas, willcontinue to apply as a matter of law forso long as an area is not attaining the 1–hour standard. Once an area attains thatstandard, however, the purpose of theprovisions of subpart 2 will have beenachieved and those provisions will nolonger apply. However, the provisionsof subpart 1 of part D of Title I of theAct would apply to the implementationof the new 8–hour O3 standards.

To facilitate the implementation ofthose provisions and to ensure a smoothtransition to the implementation of thenew 8–hour standard, the 1–hourstandard should remain applicable toareas that are not attaining the 1–hourstandard. Therefore, the 1–hourstandard will remain applicable to anarea until EPA determines that it hasattained the 1–hour standard, at whichpoint the 1–hour standard will nolonger apply to that area.

C. Communication of Public HealthInformation

Information on the public healthimplications of ambient concentrationsof criteria pollutants is currently madeavailable primarily through two EPAprograms. The first program is designedto prevent ambient pollutantconcentrations from reaching thesignificant harm level (i.e., an exposurelevel that constitutes an imminent andsubstantial endangerment to publichealth). The second program is thePollutant Standards Index (PSI),24

which is a health advisory system. Theproposal focused on the potentiallyexpanded use of the PSI in regard toallowing sensitive individuals to reducetheir risk of exposure. Currently, EPAand local officials use the PSI as apublic information tool to advise thepublic about the general health effectsassociated with different pollutionlevels and to describe whateverprecautionary steps may need to betaken if air pollution levels rise into theunhealthful range. By notifying thepublic when a PSI value exceeds 100(which corresponds to the NAAQS foreach criteria pollutant)25, citizens aregiven the opportunity to takeappropriate steps to avoid exposures ofconcern. This use of the PSI could beexpanded to provide more specifichealth information for O3 concentrations


close to the level of the primarystandard. Given the continuum of risksassociated with exposure to O3, thisinformation, while perhaps of interest toall citizens, would be particularly usefulto those individuals who are extremelysensitive to relatively low O3

concentrations. As an example, theproposal mentioned the possibility ofexpanding the PSI to include two newdescriptive categories in the Index, oneincluding concentrations within a rangesomewhat below the level of the newprimary standard (with a possibledescriptor of ‘‘moderately good’’), theother including concentrations within arange somewhat above the level of thestandard (with a possible descriptor of‘‘moderately unhealthful’’). Such anapproach could better reflect theincreased understanding of healtheffects associated with O3 exposuredeveloped during this review, andwould be consistent with therecommendation of a number of CASACpanel members ‘‘that an expanded airpollution warning system be initiated sothat sensitive individuals can takeappropriate ’exposure avoidance’behavior’’ (Wolff, 1995b).

The proposal also discussed the use offorecasting in combination with thisexpanded use of the PSI. For a healthadvisory system to be effective, citizensneed to be notified as early as possibleto be able to avoid exposures of concern.The notice indicated that if the current1–hour primary NAAQS for O3 isreplaced with an 8–hour standard, therewould clearly be increased value inusing forecasted O3 concentrations inproviding cautionary statements to thepublic. Currently, when a healthadvisory indicates that the 1–hour O3

PSI value of 100 has been exceeded,citizens generally have time to avoidexposures of concern because O3 levelstend to remain elevated for severalhours during the day. With the new 8–hour standard, however, this wouldlikely not be the case, since by the timea PSI value is reported, the potential forprolonged exposures of concern wouldlikely have passed for that day.Forecasting 8–hour maximum O3

concentrations would facilitate the risk-reduction function of the PSI by givingcitizens more time to limit or avoidexposures of concern.

The EPA did not formally proposerevisions to the PSI in the proposal.Instead, the Administrator requestedcomment, and indicated that the Agencymight propose revisions to the PSI inconjunction with future proposalsassociated with the implementation of arevised NAAQS.

The EPA received a large number ofcomments from a wide variety of

commenters on the usefulness of bothan expanded health advisory systemand the forecasting of 8–hour ambientO3 concentrations. Commentersrepresenting State and local agencies,business and industry associations, aswell as environmental associationsoverwhelmingly endorsed the use of anexpanded public health advisory systemand many noted the importance offorecasting 8–hour O3 concentrations inconjunction with the PSI, whilerecognizing a number of issues thatwould need to be addressed.

Comments from environmentalassociations endorsed increasing thespecificity of warnings with regard tothe health effects that could occur as aresult of exposure, and noted thatcitizens are capable of dealing withcomplex information. Thesecommenters also took exception todescribing O3 levels around the level ofthe standard that have been shown toresult in decreased lung function andincreased respiratory symptoms, as‘‘moderately good,’’ stating that thisdescriptor is misleading and might notbe heeded by people who could, if theyfully understood the nature of the healthrisk, take action to minimize theirexposures. Other commenters felt thatthe descriptors ‘‘moderately good’’ and‘‘moderately unhealthful’’ wereunnecessarily confusing.

Industry commenters were uniformlysupportive of enhancing the riskreduction function of the PSI by issuinghealth advisories with specific healthinformation at and above the level of thestandard. Several industry commentersalso recommended that the function ofthe PSI be combined with the functionof an O3 action system, which wouldrecommend voluntary actions to reduceambient O3 concentrations when thelevel of the standard is forecasted to beexceeded. This would result in a systemthat not only could provide accuratehealth effects information specific to themembers of the population likely toexperience effects, but also could helpprevent exposures to levels of O3 at orabove the level of the standard.

Commenters from State and local airpollution control authorities stronglyendorsed expanding the use of the PSIand the utilization of forecasted 8–hourO3 concentrations. These commentersencouraged EPA to develop any suchapproaches to revise the PSI inconsultation with State and localagencies, specifically in the areas ofsharing real-time O3 monitoring dataamong neighboring States, riskcommunication with the public, andcoordination of a national program.States also expressed the need forflexibility in the implementation of such

approaches and for guidance from EPAon technical aspects such as forecasting.

The EPA will take all of thesecomments into consideration whendeveloping a proposal to revise the PSI(40 CFR 58.50) for O3. The EPA plansto propose these revisions, as well asrevisions to the significant harm levelprogram (40 CFR 51.16), at a later date.

III. Rationale for the Secondary O3

Standard

A. Introduction

1. Overview. This notice presents theAdministrator’s final decision regardingthe need to revise the current secondaryO3 standard, and more specifically, toreplace the existing 1–hour, 0.12 ppmO3 secondary NAAQS with a secondarystandard equal in form, level, andaveraging time to the new 8–hour, 0.08ppm primary standard. This decision isbased on a thorough review of thescientific information on vegetationeffects associated with exposure toambient levels of O3 as assessed in theCriteria Document. This decision alsotakes into account:

(1) Staff Paper assessments of themost policy-relevant information in theCriteria Document and staff analyses ofair quality, vegetation exposure andrisk, and economic values presented inthe Staff Paper, upon which staffrecommendations for a new O3

secondary standard were based.(2) Consideration of the degree of

protection to vegetation potentiallyafforded by the new 8–hour, 0.08 ppmprimary standard compared toalternative secondary standards.

(3) CASAC advice andrecommendations as reflected indiscussion of drafts of the CriteriaDocument and Staff Paper at publicmeetings, in separate written comments,and in CASAC’s letter to theAdministrator (Wolff, 1996).

(4) Public comments received duringdevelopment of these documents eitherin conjunction with CASAC meetings orseparately.

(5) Extensive public commentsreceived on the proposed decisionregarding the secondary O3 standard.After taking this information intoaccount and for the reasons discussed inthis Unit, the Administrator concludesthat revisions to the current secondarystandard are appropriate at this time toprovide increased protection againstadverse effects to public welfare, andthat it is appropriate to set the newsecondary standard identical to the newprimary standard.

This review has focused on O3 effectson vegetation since these public welfareeffects are of most concern at O3


26 The SUM06 exposure index cumulates over agiven time period and diurnal window all hourlyO3 concentrations greater than or equal to 0.06 ppm.

concentrations typically occurring inthe United States. By affectingcommercial crops and naturalvegetation, O3 may also indirectly affectnatural ecosystem components such assoils, water, animals, and wildlife.Based on the scientific literatureassessed in the Criteria Document, theAdministrator believes it is reasonableto conclude that a secondary standardthat protects the public welfarecategories of commercial crops andnatural vegetation from known oranticipated adverse effects would alsoafford increased protection to theseother related public welfare categories.With regard to O3 effects on manmadematerials and deterioration of property,the scientific literature assessed in theCriteria Document contains little newinformation since the last review.Accordingly, EPA again concludes forthe reasons set forth in 1993 (58 FR13008, March 9, 1993) that O3-relatedeffects on materials do not provide abasis for selecting an averaging time andlevel for a secondary standard. Inaddition, since the effects of O3 onpersonal comfort and well-being (e.g.,nose and throat irritation, chestdiscomfort, and cough) have beenaccounted for in the review of theprimary standard, these effects are notconsidered in this review of thesecondary standard.

The vegetation effects information,exposure and risk assessment, andeconomic analyses presented in theStaff Paper and proposal are brieflyoutlined in the remainder of Unit III.A.of this preamble. The key issues raisedin public comments with regard to:Whether revisions to the currentsecondary standard are requisite toprotect public welfare from adverseeffects and the specific elements of arevised secondary standard arediscussed in Unit III.B. along with theAdministrator’s rationale for concludingthat it is appropriate to revise thecurrent secondary standard to beidentical to the new primary standard.

2. Vegetation effects information.Exposures to O3 have been associatedquantitatively and qualitatively with awide range of vegetation effects such asvisible foliar injury, growth reductionsand yield loss in annual crops, growthreductions in tree seedlings and maturetrees, and effects that can have impactsat the forest stand and ecosystem level.Summarized below are key findings foreach of the above effects categories thatare discussed in more detail in theCriteria Document, Staff Paper, andproposal.

Visible foliar injury can represent adirect loss of the intended use of theplant, ranging from reduced yield and/

or marketability for some agriculturalspecies to impairment of the aestheticvalue of urban ornamental species. Ona larger scale, foliar injury is occurringon native vegetation in national parks,forests, and wilderness areas, and maybe degrading the aesthetic quality of thenatural landscape, a resource importantto public welfare.

Ozone can interfere with carbon gain(photosynthesis) and allocation ofcarbon with or without the presence ofvisible foliar injury. As a result ofdecreased carbohydrate availability,remaining carbohydrates may beallocated to sites of injured tissue oremployed in other repair orcompensatory processes, thus reducingthe carbohydrates available for plantgrowth and/or yield. Growth and yieldeffects of O3 have been welldocumented for numerous species,including commodity crops, fruits andvegetables, and seedlings of bothconiferous and deciduous tree species.

Due to a number of differencesbetween seedlings and mature trees intheir responses to O3 exposures, datafrom tree seedling studies cannot, at thistime, be extrapolated to quantifyresponses to O3 in mature trees.However, long-term observationalstudies of mature trees have showngrowth reductions in the presence ofelevated O3 concentrations. Where thesegrowth reductions are not attributed toO3 alone, due to the presence of manyother environmental variables, it hasbeen reported that O3 is a significantcontributor that potentially exacerbatesthe effects of other environmentalstresses (e.g., pests). In addition, studiesshow that sensitivity to O3 with respectto visible foliar injury and growth andyield effects can vary significantlywithin and between species for bothcrops and trees.

Growth reductions can indicate thatplant vigor is being compromised suchthat the plant can no longer competeeffectively for essential nutrients, water,light, and space. When many O3-sensitive individuals make up apopulation, the whole population maybe affected. Changes occurring withinsensitive populations, or stands, if theyare severe enough, ultimately canchange community and ecosystemstructure. Structural changes that alterthe ecosystem functions of energy flowand nutrient cycling can alter ecosystemsuccession.

In the CASAC closure letter, allCASAC panel members agreed that‘‘damage is occurring to vegetation andnatural resources at concentrationsbelow the present 1–hour nationalambient air quality standard (NAAQS)of 0.12 ppm,’’ and the vegetation experts

agreed that ‘‘plants appear to be moresensitive to O3 than humans’’ (Wolff,1996). Further, the CASAC panel agreed‘‘that a secondary NAAQS, morestringent than the present primarystandard, was necessary to protectvegetation from O3’’ (Wolff, 1996). TheAdministrator concurred in the proposalwith the unanimous view of CASACthat the current standard of 0.12 ppm,1–hour average, does not provideadequate protection to vegetation fromthe adverse effects of O3, based on thefollowing specific observations thatwere taken from key studies and otherbiological effects information reportedin the O3 Criteria Document and StaffPaper:

(1) O3 concentrations ≥ 0.10 ppm canbe phytotoxic to a large number of plantspecies, and can produce acute foliarinjury responses and reduced crop yieldand biomass production.

(2) O3 concentrations within the rangeof 0.05 to 0.10 ppm have the potentialover a longer duration of creatingchronic stress on vegetation that canresult in reduced plant growth andyield, shifts in competitive advantagesin mixed populations, decreased vigorleading to diminished resistance to pestand pathogens, and injury from otherenvironmental stresses. Some sensitivespecies can experience foliar injury andgrowth and yield effects even whenconcentrations never exceed 0.08 ppm.

The Administrator further concludedthat the available scientific informationsupports the conclusion that acumulative seasonal exposure index,such as the proposed SUM06 index,26 ismore biologically relevant than a singleevent or mean index.

3. Vegetation exposure and riskanalyses. In reaching a judgment in theproposal as to a standard requisite toprotect crops and vegetation against theadverse effects of O3, the Administratortook into account several additionalconsiderations including the extent ofexposure of O3-sensitive species,potential risks of adverse effects to suchspecies, and monetized andnonmonetized categories of increasedvegetation protection associated withreductions in O3 exposures. In so doing,the Administrator recognized thatmarkedly improved air quality, and thussignificant reductions in O3 exposureswould result from attainment of thealternative 0.08 ppm, 8–hour primarystandards within the range of 1- and 5-expected exceedance forms. Thus, as amatter of policy, the Agency estimatedthe increased protection from O3-related


27 Including 15 species, representingapproximately 75% of the U.S. sales of agriculturalcrops, evaluated in the National Crop LossAssessment Network (NCLAN) studies undertakenin the early to mid-1980’s, which provide thelargest, most uniform database on the effects of O3

on agricultural crop species.28 These fruit and vegetable crops constitute

approximately 50% of the Nation’s fruits andvegetable markets.

effects on vegetation associated withattainment of alternative 8–hour, 0.08ppm primary standards, and thenconsidered the incremental protectionassociated with attainment of a seasonalsecondary standard.

The ability of EPA to characterize O3

air quality in rural and remote sites waslimited by the available rural O3

monitoring network. Therefore, EPAconducted national analyses usinggeographic information systems (GIS)and data from existing air qualitymonitoring sites to estimate seasonal O3

air quality for the year 1990, in terms ofthe 3–month, 12–hour, SUM06 exposureindex. The year 1990 was selectedbecause it was a fairly typical year interms of O3 air quality. The estimated1990 air quality was then used as abaseline from which to roll back O3

concentrations to project O3 air qualitythat would be expected to occur whenalternative standards were just attained.

The regulatory scenarios examinedincluded just attaining the existing 1–hour secondary standard, alternative 8–hour primary standards in the range of0.07 to 0.09 ppm, including standardsset at 0.08 ppm, with 1- and 5-expected-exceedance forms, and a range ofseasonal standards using the SUM06index, based on a single year of data.Estimates of air quality associated withalternative 8–hour primary standardswith 1- and 5-expected-exceedanceforms were used to roughly bound airquality estimates for 8–hour standardswith concentration-based forms rangingfrom the annual second- to the fifth-highest concentration-based forms, andincluding the proposed third-highestconcentration-based form.

By comparing these projected airquality scenarios for alternativestandards with maps showing thegrowing regions for O3-sensitive cropsand tree seedling species, estimates ofexposures of concern and risks ofadverse effects for various species weredeveloped for alternative standards.Taking into account the body ofinformation concerning O3 effects onvegetation, as presented in the CriteriaDocument and Staff Paper andsummarized in the proposal, EPAconsidered both quantifiable risks(when exposure-response functionswere available) as well as those risksthat could only be qualitativelycharacterized.

The Administrator concluded in theproposal that attaining a 8–hour, 0.08ppm primary standard within the rangeof forms under consideration wouldprovide substantially improvedprotection of vegetation from seasonalO3 exposures of concern. TheAdministrator recognized, however, that

some areas may continue to haveelevated seasonal exposures, includingforested park lands and other naturalareas and Class I areas that are federallymandated to preserve certain air qualityrelated values.

In its discussions of uncertainties,described in the proposal, the CASACPanel members expressed concernsabout the use of the GIS methodology toproject national O3 air quality andexposures of O3-sensitive species. As isthe case with other analytic methods(e.g., Krieging, inverse distanceweighting), the GIS methodologycontains numerous assumptions anduncertainties, and incorporates variousdatabases each with their own set ofuncertainties. As noted in the StaffPaper and proposal, the EPA andCASAC recognized that theuncertainties in exposure and riskestimates derived from the GISmethodology are large andunquantifiable, but that the methodprovides useful information that isappropriate to consider in comparingthe relative protection afforded byalternative standards. Further, EPAnoted in the Staff Paper and proposalthat the GIS-generated air qualityestimates compare reasonably well withthe limited available O3 monitoringdata. In taking the results from theseanalyses into account, the Administratorrecognized these inherent limitationsand primarily considered thecomparative results in assessing thedegree of protection afforded byalternative standards.

While the analyses discussed aboveindicated that an 8–hour, 0.08 ppmprimary standard within the range ofalternatives considered, would provideincreased protection for commercial andnatural vegetation, it remaineduncertain as to the extent to which airquality improvements designed toreduce 8–hour O3 concentrations wouldreduce O3 exposures measured by aseasonal SUM06 index. To furtherexplore this question, EPA alsoexamined the design values foralternative 8–hour, 0.08 ppm standards,within the range of 1- and 5-expectedexceedances, averaged over 3 years, anda 3–month, 12–hour SUM06 standardfor 581 counties (those having sufficientmonitoring data for the period 1991 –1993). As discussed in the Staff Paperand proposal, this analysis revealed thatalmost all areas that are within or abovea SUM06 range of 25–38 ppm–hourswould also have an 8–hour dailymaximum design value of greater than0.08 ppm. Thus, in those areas in whichair quality monitoring is beingconducted, areas that would likely be ofmost concern for effects on vegetation,

as measured by the SUM06 exposureindex, would also be addressed by an 8–hour primary standard set at a 0.08 ppmlevel.

4. Monetized estimates of vegetationprotection. As discussed in sectionVII.F. of the Staff Paper and in theproposal, EPA developed monetizedestimates of increased protectionassociated with several alternativestandards for economically importantcommodity crops nation-wide27 and forfruit and vegetable crops in California.28

These analyses were based on the GIS-generated projections of O3 air qualityfor various alternative standards.Monetized estimates of increasedprotection could not be developed forother important categories of vegetation,such as urban ornamentals, Class Iareas, and commercial and other forestsbecause of a lack of availableconcentration-response functions andappropriate economic valuation models.The available data suggested, however,that reductions in ambient O3

concentrations resulting fromattainment of alternative standardswould confer increased protection forthese categories as well by reducingbiomass loss, protecting functional,aesthetic, and existing values, and bypreserving biodiversity and nativehabitats.

As summarized in the proposal, mostof the monetized estimates of increasedprotection would accrue fromattainment of an 8–hour, 0.08 ppmprimary standard, with a smallerincremental improvement obtained bythe addition of a seasonal secondarystandard. In contrast, the incrementalprotection obtained from the addition ofa seasonal secondary standard would beconsiderably more significant whencompared to an alternative 8–hourprimary standard at a level of 0.09 ppm.

B. Need for Revision of the CurrentSecondary Standard

Based on the above considerationsand the rationale in the proposal, theAdministrator proposed and soughtcomment on two alternative standards,either of which in her judgment wouldbe appropriate to protect public welfarefrom known or anticipated adverseeffects given the available scientificknowledge. The two alternatives weresetting the revised secondary standard


identical to the proposed 8–hour, 0.08ppm primary standard, or establishing a3–month, 12–hour, SUM06 seasonalsecondary standard at the level of 25ppm–hours. The Administratorrecognized that it would be a reasonablepolicy choice to set the revisedsecondary standard identical to an 0.08,8–hour ppm primary standard, but alsorecognized that a SUM06 seasonalstandard is more biologically relevantand, therefore, was also appropriate toconsider.

In reaching her final decision on arevised secondary standard, theAdministrator has taken into accountseveral factors. First, she againconcludes based on informationpresented in the Criteria Document andStaff Paper, and summarized in theproposal and in this preamble, that theexisting secondary standard does notprovide adequate protection forvegetation against the adverse welfareeffects of O3.

Second, she has considered thecomments made by the CASAC Panelmembers during their reviews of thesedocuments and in CASAC’s closureletter, ‘‘that a secondary NAAQS, morestringent than the present primarystandard, was necessary to protectvegetation from O3’’ (Wolff, 1996).These statements provide strong supportto the Administrator’s judgment that thebody of scientific evidence on O3 effectson vegetation provides sufficient andcompelling evidence that the currentsecondary standard is not adequatelyprotective and should be revised.

Third, the Administrator recognizesthat significant uncertainties remainwith respect to exposure dynamics, airquality relationships, and estimates ofincreased vegetation protection whichare important factors in selecting anappropriate secondary standard, asdescribed more fully in the CriteriaDocument, Staff Paper and proposal.The CASAC closure letter highlightedkey uncertainties that hampered thePanel’s ability to make anyrecommendations as to an appropriateform or level for a secondary standardthat would be protective against adverseeffects on vegetation from exposure toambient levels of O3. The Panel statedthat ‘‘agreement on the level and formof such a standard is still elusive’’ and‘‘***there remain important limitationsto our understanding of the extent of theresponse of vegetation to O3 under fieldconditions’’ (Wolff, 1996). Theseuncertainties are largely a result ofinadequate rural and remote O3 airquality data that would allow withgreater certainty determination of therelationships between O3-related effectsbeing observed in the field and ambient

O3 exposures. Nevertheless, thealternative standards proposed by theAdministrator are consistent with therange of views expressed by the CASACpanel members, and CASAC recognizedthat choosing between the twoalternatives is a policy decision thatcannot be based solely on science(Wolff, 1996).

Fourth, the Administrator recognizedthat just attaining the 8–hour, 0.08 ppm,1- and 5-expected exceedancealternatives results in markedlyimproved air quality when compared tojust attaining the existing secondarystandard, with only slightimprovements associated with goingfrom a 5- to 1-expected exceedanceform.

Fifth, the Administrator has carefullyconsidered the information and viewsprovided in the public comments.Though these comments yielded no newscientific information relevant tochoosing between the two alternativeproposed standards, many commentersrepeated the CASAC’s concerns over thesignificant uncertainties remaining inthe database. Many of these commentersexpressed the view that EPA shouldwait to set a seasonal secondarystandard until better rural air qualitydata were available, which would allowfor better characterization of themagnitude of improvements in publicwelfare protection likely to be affordedby such a standard compared to arevised primary standard.

In sharp contrast, other commentersexpressed the view that the availabledata were sufficient to demonstrate aneed to set a seasonal secondarystandard to protect vegetation againstthe adverse effects of O3, and many suchcommenters recommended theproposed SUM06 form for such astandard. A significant number of thesecommenters also maderecommendations on the appropriatelevel for a seasonal SUM06, generallyrecommending levels lower than theproposed 25 ppm-hours, ranging from 8to 20 ppm–hours. The key sourcefrequently cited in support of theserecommendations is an article by Heckand Cowling (1997) which summarizesthe outcome of a consensus-buildingworkshop sponsored by the SouthernOxidant Study group on the secondarystandard held in January 1996.

This workshop was attended by 16scientists with backgrounds inagricultural, managed forest, naturalsystems, and air quality, all of whom areleaders in their fields and whoseresearch formed the basis of much of theresearch examined in the CriteriaDocument. These scientists expressedtheir judgements on what standard

level(s) would provide vegetation withadequate protection from O3-relatedadverse effects.

Though the report identified no newdata in support of the scientists’recommendations, the Administratorbelieves that the report lends importantsupport to the view that the currentsecondary standard is not adequatelyprotective of vegetation. Further, theAdministrator believes that the reportforeshadows the direction of futurescientific research in this area, theresults of which could be important infuture reviews of the O3 secondarystandard.

As the results of such researchbecome available, EPA will be in abetter position to characterize rural airquality and the improvements invegetation protection that would resultfrom a seasonal secondary standard, andto select a standard level that wouldprovide adequate protection forvegetation. However, given the presentlimits of the scientific evidence of O3-related effects and of rural air qualitydata, as discussed in the CriteriaDocument, Staff Paper, the proposal,and by CASAC, the Administrator hasdecided that it is not appropriate tomove forward with a seasonal secondarystandard at this time for the reasonsdescribed below. In coming to thisconclusion, the Administratorspecifically considered the significantimprovements in public welfareprotection that are expected to beafforded by the new 8–hour primarystandard, as well as the value ofobtaining additional information tobetter characterize O3-related effects onvegetation under field conditions.

C. Final Decision on the SecondaryStandard

Based on the scientific evidence,CASAC advice and recommendations,comments received on the proposal, andthe considerations summarized above,the Administrator is replacing thecurrent secondary O3 standard with an8–hour standard, set at a level of 0.08ppm, identical in all respects to the newprimary standard. The Administratorjudges that this standard will providesubstantially improved protection forvegetation from O3-related adverseeffects as compared to that provided bythe current 1–hour, 0.12 ppm secondarystandard, while allowing time foradditional research and thedevelopment of a more complete ruralmonitoring network and air qualitydatabase from which to evaluate theelements of an appropriate seasonalsecondary standard.

The decision not to set a seasonalsecondary standard at this time is based


29 36 FR 8186, Apr. 30, 1971. EPA has maintainedthis interpretation consistently since then.

in large part on the Administrator’srecognition that the exposure, risk, andmonetized valuation analyses presentedin the proposal contain substantialuncertainties, resulting in only roughestimates of the increased publicwelfare protection likely to be affordedby each of the proposed alternativestandards. These uncertainties werediscussed in the proposal and the StaffPaper and were noted by CASAC (Wolff,1996). In light of these uncertainties, theAdministrator has decided it is notappropriate at this time to establish anew separate seasonal secondarystandard given the potentially smallincremental degree of public welfareprotection that such a standard mayafford. Instead, the Administrator findsit a reasonable policy choice to set anew secondary standard identical to thenew primary standard, while focusingadditional research on key areas forconsideration in the next review of theO3 criteria and standards.

Continued research on the effects ofO3 on vegetation under field conditionsand on better characterizing therelationship between O3 exposuredynamics and plant response will beimportant in the next review because:

(1) The available biological databasehighlights the importance ofcumulative, seasonal exposures as aprimary determinant of plant responses.

(2) The association between dailymaximum 8–hour O3 concentrationsand plant responses has not beenspecifically examined in field tests.

(3) The impacts of attaining an 8–hour, 0.08 ppm primary standard inupwind urban areas on rural air qualitydistributions cannot currently becharacterized with confidence due tolimited monitoring data and air qualitymodeling in rural and remote areas.

Setting the secondary standard equalto the primary standard will allow EPAthe opportunity to evaluate morespecifically the improvement in rural airquality and in O3-related vegetationeffects resulting from measures designedto attain the new primary standard. Thisinformation in turn will allow for betterevaluation of the incremental need for aseparate seasonal secondary standard inthe next review of the O3 criteria andstandards.

In the proposal, the Administratorsolicited comment on the appropriatespatial scale of an expanded ruralmonitoring network. Relatively fewcomments were received regarding anexpanded rural monitoring network, butthose who did submit comments weregenerally in favor of an expandednetwork to allow for improvedmodelling of long-range transport of O3

and its precursors and for better

characterization of O3 air quality inrural and remote areas. Those commentswill serve to inform EPA’s developmentof revised air quality surveillancerequirements (40 CFR part 58) that willbe proposed at a later date.

With respect to the proposed seasonalsecondary standard only, the proposalsought comment on whether O3

concentrations from several monitorsshould be spatially integrated whendetermining compliance with thestandard. Only a few comments werereceived, with some supporting andsome opposing spatial integration of O3

concentrations from several monitors.In view of the Administrator’s

decision to replace the currentsecondary standard with a secondarystandard which is identical in form,level, and averaging time to the new 8–hour, 0.08 ppm primary standard, ratherthan with a seasonal standard, EPA isnot adopting the use of spatial averagingfor the new secondary standard.

To decrease some of the uncertaintiesdiscussed above and to remedy the lackof air quality data in rural and remoteareas of commercial or ecologicalimportance for vegetation, theAdministrator reiterates her intention,expressed in the proposal, to expand therural O3 monitoring network. The EPAwill propose revised O3 air qualitysurveillance requirements (40 CFR part58) at a later date. The EPA is exploringopportunities to work with otherFederal agencies to develop acoordinated and long-term ruralmonitoring network.

IV. Other IssuesSeveral commenters raised key legal

and procedural issues that are discussedbelow. These include: (1) Whether EPAmust give consideration to costs andsimilar factors in setting NAAQS; (2)whether EPA erred in its selection of amethodology for determining the levelof a NAAQS that protects public healthwith an adequate margin of safety; (3)whether EPA committed a proceduralerror by not extending the commentperiod; and (4) whether the 1990amendments to the Act preclude EPAfrom revising the O3 NAAQS toestablish a new 8–hour standard.Responses to other legal and proceduralissues are included in the Response-to-Comments Document.

A. Cost ConsiderationsFor more than a quarter of a century,

EPA has interpreted section 109 of theAct as precluding consideration of theeconomic costs or technical feasibilityof implementing NAAQS in settingthem. As indicated in the proposal, anumber of judicial decisions have

confirmed this interpretation. NaturalResources Defense Council v.Administrator, 902 F.2d 962, 972–73(D.C. Cir. 1990)(PM NAAQS)(‘‘PM10’’),vacated, in part, dismissed, 921 F.2d326 (D.C. Cir.), certs. dismissed, 498U.S. 1075, and cert. denied, 498 U.S.1082 (1991); Natural Resources DefenseCouncil v. EPA, 824 F.2d 1146, 1157–59(D.C. Cir. 1987)(en banc)(CAA section112 standards for vinyl chloride)(‘‘VinylChloride’’); American PetroleumInstitute v. Costle, 665 F.2d 1176, 1185–86 (D.C. Cir. 1981)(ozoneNAAQS)(‘‘Ozone’’), cert. denied, 455U.S. 1034 (1982); Lead Industries Ass’nv. EPA, 647 F.2d 1130, 1148–51 (D.C.Cir.)(lead NAAQS)(‘‘Lead Industries’’),cert. denied, 449 U.S. 1042 (1980).

Some commenters have argued thatcosts and similar factors should,nonetheless, be considered, both in thisrulemaking and in the rulemaking onproposed revisions to the NAAQS forparticulate matter. Although most of thecommenters’ arguments are inconsistentwith the judicial decisions cited above,several commenters have argued thatthose decisions are not dispositive. Forreasons discussed below and in theResponse-to-Comments Document, EPAdisagrees with these comments andmaintains its longstandinginterpretation of the Act as precludingconsideration of costs and similarfactors in setting NAAQS.

1. Background. Given the nature ofthe points raised, a brief review of theissue seems useful before addressing thecomments. The requirement that EPAestablish national ambient air qualitystandards for certain pollutants, to beimplemented by the States, was enactedin 1970 as part of a set ofcomprehensive amendments thatestablished the basic framework forFederal, State, and local air pollutioncontrol. When EPA promulgated theoriginal NAAQS in 1971, its firstAdministrator, William D. Ruckelshaus,concluded that costs and similar factorscould not be considered in thatdecision.29 This conclusion was notchallenged in litigation on the originalNAAQS. It has been confirmed sincethen, however, by every judicialdecision that has considered the issue.

As discussed below, EPA’sinterpretation rests primarily on thelanguage, structure, and legislativehistory of the statutory scheme adoptedin 1970. It is also supported by thejudicial decisions cited above, as well asby legislative developments since 1970that reaffirm Congress’ originalapproach to the issue.


30 That consideration of such factors was notintended in NAAQS decisions is also supported bysection 109(a)(1). For pollutants for which airquality criteria had been issued prior to the 1970amendments, that provision required EPA topropose NAAQS within 30 days after enactmentand to take final action 90 days later. The criteriaissued previously did not include information oncosts and similar factors, and it would have beendifficult if not impossible for EPA to supplementthem in time to include meaningful considerationof such factors in NAAQS proposed 30 days afterenactment.

31 See, e.g., sections 110(e)(1), 111(a)(1), 231(b)(1970 Act); see also, e.g., sections 113(d)(4)(C)(ii),125(a)(3), 202(a)(3)(C), 317 (1977 Act).

32 Union Electric Co. v. EPA, 427 U.S. 246, 257–58 (1976).

33 The Senate report on the 1970 amendmentsstated: ‘‘In the Committee discussions, considerableconcern was expressed regarding the use of theconcept of technical feasibility as the basis ofambient air standards. The Committee determinedthat (1) the health of people is more important thanthe question of whether the early achievement ofambient air quality standards protective of health istechnically feasible; and, (2) the growth of pollutionload in many areas, even with application ofavailable technology, would still be deleterious topublic health.’’

‘‘Therefore, the Committee determined thatexisting sources of pollutants either should meetthe standard of the law or be closed down ***.’’

S. Rep. No. 91–1196, at 2–3 (1970).

34 These limitations would, of course, make littlesense if such factors could be considered in settingthe NAAQS themselves.

35 Such requirements ‘‘ ‘are expressly designed toforce regulated sources to develop pollution controldevices that might at the time appear to beeconomically or technologically infeasible.’ ’’ Id.(quoting Union Electric Co. v. EPA, 427 U.S. at 257).

36 In the PM10 case, for example, the Courtconsidered an argument that EPA should haveconsidered potential health consequences ofunemployment that might result from revision ofthe primary NAAQS for PM:

‘‘This claim is entirely without merit. In threeprevious cases, this court has emphatically statedthat section 109 does not permit EPA to considersuch costs in promulgating national ambient airquality standards ***. It is only health effectsrelating to pollutants in the air that EPA mayconsider . *** Consideration of costs associatedwith alleged health risks from unemploymentwould be flatly inconsistent with the statute,legislative history and case law on this point.’’

902 F.2d at 973 (emphasis in original; citationsomitted).

37 See, e.g., H.R. Rep. No. 95–294, at 207–17(l977).

38 See, e.g., id. at 110–12; id. at 43–51.

Without cataloguing all relevantaspects of the 1970 amendments andtheir legislative history, several basicpoints should be noted. Under section109(b) of the Act, NAAQS are to be‘‘based on’’ the air quality criteria issuedunder section 108. Under section108(a)(2), the kind of information EPAis required to include in criteriadocuments is limited to informationabout health and welfare effects ‘‘whichmay be expected from the presence of[a] pollutant in the ambient air ***.’’There is no mention of the costs ordifficulty of implementing the NAAQS,nor of ‘‘effects’’ that might result fromimplementing the NAAQS (as opposedto effects of pollution in the air).30 Bycontrast, Congress explicitly providedfor consideration of costs and similarfactors in decisions under other sectionsof the Act.31 Moreover, States werepermitted to consider economic andtechnological feasibility in developingplans to implement the NAAQS to theextent such consideration did notinterfere with meeting statutorydeadlines for attainment of thestandards.32 Finally, the legislativehistory indicated that Congress hadconsidered the issue and haddeliberately chosen to mandate NAAQSthat would protect health regardless ofconcerns about feasibility.33

The first judicial decision on the issuecame in the Lead Industries case. Anindustry petitioner argued that EPAshould have considered economic andtechnological feasibility in allowing a‘‘margin of safety’’ in setting primary

standards for lead. Based on a detailedreview of the language, structure, andlegislative history of the statutoryscheme, the U.S. Court of Appeals forthe District of Columbia Circuitconcluded that:

This argument is totally without merit.[The petitioner] is unable to point toanything in either the language of the Act orits legislative history that offers any supportfor its claim ***. To the contrary, the statuteand its legislative history make clear thateconomic considerations play no part in thepromulgation of ambient air qualitystandards under section 109.

647 F.2d at 1148.The Court cited a number of reasons

for this conclusion. Id. at 1148–50.Among other things, it noted thecontrast between section 109(b) andother provisions in which Congress hadexplicitly provided for consideration ofeconomic and technological feasibility,as well as the requirement that NAAQSbe based on air quality criteria definedwithout reference to such factors. Id. at1148–49 & n.37. The Court also notedthat, in developing plans to implementNAAQS, States may consider economicand technological feasibility only to theextent that this does not interfere withmeeting the statutory deadlines forattainment of the standards; and thatEPA may not consider such factors at allin deciding whether to approve Stateimplementation plans. Id. at 1149 n.37(citing Union Electric Co. v. EPA, 427U.S. 246, 257–58, 266 (1976)).34

As to the legislative history of the1970 amendments, the Court observedthat:

[T]he absence of any provision requiringconsideration of these factors was noaccident; it was the result of a deliberatedecision by Congress to subordinate suchconcerns to the achievement of health goals.

Id. at 1149. Citing several leadingSupreme Court decisions, as well as theSenate report quoted above, the Courtnoted that Congress had intended adrastic change in approach toward thecontrol of air pollution in the 1970amendments and was well aware thatsections 108–110 imposed requirementsof a ‘‘technology-forcing’’ character.Id.35

The Court also noted that Congresshad already acted, in furtheramendments adopted in 1977, to relievesome of the burdens imposed by the1970 amendments. Id. at 1150 n.38.

Observing that Congress had, however,declined to amend section 109(b) toprovide for consideration of costs andsimilar factors as requested by industrialinterests, id. n.39, the Court concluded:

A policy choice such as this is one whichonly Congress, not the courts and not EPA,can make. Indeed, the debates on the [1970amendments] indicate that Congress wasquite conscious of this fact***.

*** [I]f there is a problem with theeconomic or technological feasibility of thelead standards, [the petitioner], or any otherparty affected by the standards, must take itscase to Congress, the only institution withthe authority to remedy the problem.

Id. at 1150.After the decision in Lead Industries,

Supreme Court review was sought onthe question whether costs and similarfactors could be considered in settingNAAQS, among other issues. TheSupreme Court declined to review thedecision. Lead Industries Ass’n v. EPA,449 U.S. 1042 (1980). The subsequentdecisions in Ozone, Vinyl Chloride, andPM10, cited above, strongly reaffirmedthe interpretation adopted in LeadIndustries.36 Supreme Court review ofthe Ozone and PM10 decisions wassought but denied. American PetroleumInstitute v. Gorsuch, 455 U.S. 1034(1984); American Iron and SteelInstitute v. EPA, 498 U.S. 1082 (1991).

The Lead Industries opinion focusedlargely, though not exclusively, on the1970 amendments and their legislativehistory. Perhaps as a result, it did notcanvass all the factors that, in fact,supported its conclusions at the time.For example, when Congress enactedmajor amendments to the Act in 1977,it was clearly aware that some areas ofthe country had experienced difficultyin attempting to attain some of theNAAQS.37 It was also aware that theremight be no health-effects thresholds forthe pollutants involved, and thatsignificant uncertainties are inherent insetting health-based standards under theAct.38 In response, Congress made


39 Section 109(d)(2)(C)(iv). Some commentershave argued that this provision requires EPA toconsider such effects in setting NAAQS. From thelanguage and structure of section 109(d), however,it is clear that CASAC’s responsibility to advise onthese factors is separate from its responsibility toreview and recommend revision of air qualitycriteria and NAAQS, and that the advice pertainsto the implementation of NAAQS rather than tosetting them. The legislative history confirms thisview, indicating that the advice was intended forthe benefit of the States and Congress. See H.R. Rep.No. 95–294, at 183 (1977).

40 The 1977 amendments also required EPA toprepare economic impact assessments for specifiedactions but limited the requirement to non-health-based standards, excluding decisions undersections 109 and 112. Section 317; H.R. Rep. No.95–294, at 51–52 (1977). In this and other respects,Congress continued the approach it took in the l970amendments, making careful choices as to whenconsideration of costs and similar factors would berequired and giving paramount priority toprotection of health. See 123 Cong. Rec. H8993(daily ed. Aug. 4, 1977) (Clean Air ConferenceReport (1977); Statement of Intent; Clarification ofSelect Provisions), reprinted in 3 Senate Committeeon Environment and Public Works, 95th Cong., ALegislative History of the Clean Air ActAmendments of 1977, at 319 (1978).

41 In the interim, the National Commission on AirQuality had also submitted its report to Congress asrequired by a provision of the 1977 amendments.Among other things, the Commission recommendedthat the statutory approach of requiring NAAQS tobe set at levels necessary to protect public health,without consideration of economic factors, becontinued without change. National Commission onAir Quality, To Breathe Clean Air 55 (1981).]

42 As the Administrator indicated in EPA’sproposal to revise the PM standards:

‘‘[T]hat review has revealed a highly limited database—particularly where quantitative studies areconcerned—and a wide range of views amongqualified professionals about the exact pollutionlevels at which health effects are likely to occur.The setting of an ‘adequate margin of safety’ belowthese levels calls for a further judgment—in an areafor which the scientific data base is even moresparse and uncertain***.’’

‘‘[L]ong and expert review of public health issueshas to date revealed no scientific method ofassessing exactly what level of standards publichealth requires. The scientific review indicatessubstantial uncertainties concerning the health risksassociated with lower levels of particulate matter.’’

49 FR 10408, 10409, Mar. 20, l984.43 Congress was clearly aware of the 1987

decision to revise the PM NAAQS, which amongother things involved changing the indicator forparticulate matter from ‘‘total suspendedparticulate’’ to PM10, because it enacted specialnonattainment provisions, as well as provisions forPSD increments, applicable to PM10. Sections 188–190; section 166(f). It was clearly aware of the VinylChloride decision because it amended section 112in response to that decision, essentially creating anew scheme for setting emission standards forhazardous pollutants.

44 H.R. Rep. No. 101–490, pt. 1, at 145 (1990). Seealso S. Rep. No. 101–228, at 5 (1989).

45 Additional responses to points raised by thiscommenter and others are included, as appropriate,in the Response-to-Comments document.

46 Several other commenters argue that the citeddecisions are not dispositive because they held onlythat EPA is not required to consider costs andsimilar factors in setting NAAQS. As discussedbelow in connection with Chevron, however, thedecisions clearly concluded that Congress intendedto preclude consideration of such factors, and thatEPA is not free to alter that congressional choice.Although these conclusions are technically dicta,nothing in the Court’s opinions suggests that itwould have interpreted section 109 differently hadEPA claimed authority to consider costs and similarfactors in NAAQS decisions. Indeed, the tone of theopinions argues to the contrary. See, e.g., PM10, 902F.2d at 973. Cf. Ethyl Corp. v. EPA, 51 F.3d 1053(D.C. Cir. 1995).

47 See, e.g., Lead Industries, 647 F.2d at 1146–47,1153–56, 1160–61, 1167 n.106. In enacting the 1970amendments, Congress was aware that there weregaps in the scientific information available then asa basis for establishing the original NAAQS. See,e.g., S. Rep. No. 91–1196, at 9–11 (1970). Ifanything, Congress had an even greaterunderstanding of the point when it enacted that1977 amendments without changing the substantivecriteria for setting NAAQS. See H.R. Rep. No. 95–294, at 43–51, 181–82 (1977).

significant changes in the provisions forimplementation of the NAAQS,including changes intended to ease theburdens of attainment. It also amendedsections 108 and 109 in several ways;for example, by requiring periodicreview and, if appropriate, revision ofair quality criteria and NAAQS and byestablishing a special scientific advisorycommittee (CASAC) to advise EPA onsuch reviews. Notably, Congressrecognized that implementation ofNAAQS could cause ‘‘adverse publichealth, welfare, social, economic, orenergy effects’’ and charged CASACwith advising EPA on such matters.39

Yet it made no changes in sections109(b) or 108(a)(2); that is, in thesubstantive criteria for setting orrevising NAAQS. In other words,Congress chose to address economic andother difficulties associated withattainment of the NAAQS by adjustingthe scheme for their implementation,rather than by changing the instructionsfor setting them.40

Congress enacted major amendmentsto the Act again in 1990, well after theLead Industries and Ozone decisionsthat interpreted section 109 asprecluding consideration of costs inNAAQS decisions.41 In doing so,Congress was clearly aware ofintervening developments such as EPA’sdecision to revise the PM NAAQS in1987—the result of an elaborate review

in which the Administrator stronglyunderscored the scientific uncertaintiesinvolved42—and the Vinyl Chloride casedrawing a sharp distinction betweensections 109 and 112 with regard toconsideration of costs and similarfactors.43 Indeed, the legislative historyof the 1990 amendments reflectsCongress’ understanding that primaryNAAQS were to be based on protectionof health ‘‘without regard to theeconomic or technical feasibility ofattainment.’’44 Again, however,Congress chose to respond to severe,widespread, and persistent problemswith attaining the NAAQS by adjustingthe scheme for their implementationrather than by changing the basis forsetting them. See, e.g., sections 181–192.

2. Public comments. As notedpreviously, a number of commentershave argued that costs and similarfactors should be considered in EPA’sfinal decisions on revision of both theozone and particulate NAAQS. Asidefrom arguments that are simplyinconsistent with the judicial decisionscited above, some of the commentersargue that those decisions are notdispositive for a variety of reasons. Onecommenter submitted a particularlycomprehensive version of this argumentin the rulemaking on proposed revisionsto the particulate NAAQS; the followingdiscussion focuses primarily on pointsraised by that commenter, amongothers.45

As a general matter, the commenteracknowledges that Congress intended to

preclude consideration of economiccosts and similar factors in settingNAAQS. The commenter argues,however, that this is so only when thescientific basis for NAAQS is ‘‘clear andcompelling’’ or ‘‘unambiguous.’’ Fromthat premise, the commenter advancesthree key assertions:

(1) Where non-threshold pollutantsare involved and the health evidence isambiguous, section 109 must beinterpreted to allow consideration of allrelevant factors, including the practicalconsequences of EPA’s decisions;

(2) To the extent the judicial decisionscited above are read as precluding this,they rest on a faulty analysis that pre-dates and cannot survive scrutiny underChevron, U.S.A. v. Natural ResourcesDefense Council, 467 U.S. 837 (1984);46

and(3) Because EPA has discretion to

consider costs and similar factors wherethe health evidence is ambiguous, itmust do so in light of Executive Order12866, 58 FR 51735, Oct. 4, 1993, andtwo recent statutes, the UnfundedMandate Reform Act of 1995, 2 U.S.C.secs. 1501–1571 (UMRA), and the SmallBusiness Regulatory EnforcementFairness Act of 1996, Pub. L. No. 104–121, 110 Stat. 857 (SBREFA), which inpart amended the Regulatory FlexibilityAct, 5 U.S.C. secs. 601–808.

EPA believes all three assertions areclearly incorrect. Regarding the firstpoint, it should be evident, both fromprevious NAAQS decisions and fromthe court opinions upholding them, thatthe scientific basis for NAAQS decisionshas never pointed clearly andunambiguously to a single ‘‘rightanswer.’’47 This is inherent in thestatutory scheme for the establishmentand revision of NAAQS, which in effectrequires them to be based on the ‘‘latest


48 Lead Industries, 647 F.2d at 1147 (quotingEthyl Corp. v. EPA, 541 F.2d 1, 24–27 (D.C. Cir.)(en banc), cert. denied, 426 U.S. 941 (1976)).

49 They may have methodological flaws, forexample, but nonetheless report effects that are ofserious medical significance; or they may be ofimpeccable quality but involve effects of uncertainsignificance. Others may involve results that arestriking but hard to explain in terms of previousknowledge, or results that seem plausible andimportant but are not yet replicated by otherstudies.]

50 See, e.g., Lead Industries, 647 F.2d at 1155–56;H.R. Rep. No. 94–295, at 43–51 (1977).

51 As previously discussed, the Administratorstrongly emphasized the uncertainties involved inthat review. As a result of the uncertainties, heproposed ‘‘relatively broad’’ ranges for comment,though he focused on lower levels within the rangesas providing greater margins of safety against thehealth risks involved. See 49 FR 10408, 10409, Mar.20, l984.

52 See, e.g., Lead Industries, 647 F.2d at 1152–53& n. 43, 1159–60; Ozone, 665 F.2d at 1185, 1187;PM10, 902 F.2d at 969–71, 972.

53 Indeed, the present decisions on the NAAQSfor PM and ozone are based on some of the bestscientific information the Agency has ever beenable to rely on in NAAQS decision-making. Inparticular, the science underlying these decisions ismuch more extensive and of much better qualitythan the science underlying the existing NAAQS forPM and ozone.

54 In practice, analysis of this question issometimes referred to as a ‘‘Chevron step one’’analysis.

55 See, e.g., 647 F.2d at 1148–51, 1152–53 & n.43,1160–61.

scientific knowledge’’ on potentialhealth and welfare effects of thepollutant in question. See sections109(b), 108(a)(2). Although advances inscience increase our understanding ofsuch effects, they also raise newquestions. For this reason, the keystudies for any given decision onrevision of a NAAQS are, almost bydefinition, ‘‘at the very ‘frontiers ofscientific knowledge.’ ’’48 That is,studies that call into question theadequacy of a standard are always thosethat go beyond previous studies—byreporting new kinds of effects, forexample, or effects at lowerconcentrations than those at whicheffects have been reported previously.

As with pioneering work in otherfields, such studies may have a varietyof strengths and limitations.49 As aresult, the validity and implications ofsuch studies may be both uncertain andhighly controversial. Given theprecautionary nature of section 109,50

however, it is precisely these kinds ofstudies that the Administrator mustgrapple with when advances in sciencesuggest that revision of a NAAQS isappropriate.

As a result, the EPA staff typicallyrecommends for consideration, and theAdministrator may propose forcomment, a range of alternatives basedon what the commenter would call‘‘ambiguous’’ science. In this respect,the current reviews of the NAAQS forozone and particulate matter are notunusual and do not differ, for example,from the review that led to adoption ofthe PM10 NAAQS in 1987.51 Indeed, theNAAQS that were upheld in the LeadIndustries, Ozone, and PM10 decisionswere all based on highly controversialhealth evidence; the Lead Industriesdecision took note of congressionalstatements recognizing that there maybe no thresholds for criteria pollutants;and the Ozone and PM10 decisionsnoted the Administrator’s findings that

clear thresholds could not be identifiedfor ozone and particulate matter,respectively.52 Thus, the presentdecisions on revision of the NAAQS forozone and particulate matter cannot bedistinguished from those past decisionsin terms of the nature of the healthevidence or pollutants involved.53

Regarding the second of thecommenter’s key assertions, EPAbelieves it is clear that the judicialdecisions cited above were correctlydecided and continue to be good lawunder Chevron. In Chevron, theSupreme Court essentially reaffirmedthe principle that courts must defer toreasonable agency interpretations of thestatutes they administer where Congresshas delegated authority to them toelucidate particular statutoryprovisions. Where the intent of Congresson an issue is clear, however, it must begiven effect by the agency and thecourts. See 467 U.S. at 842–45. Thus,the first question on review of anagency’s interpretation under Chevronis ‘‘whether Congress has directlyspoken to the precise question at issue.’’If the court determines that it has not,the remaining question for the court is‘‘whether the agency’s answer is basedon a permissible construction of thestatute.’’ 467 U.S. at 842–43 (footnoteomitted). In determining whetherCongress ‘‘had an intention on theprecise question at issue,’’ a courtemploys ‘‘traditional tools of statutoryconstruction.’’ Id. at 843 n.9.54

In essence, the commenter’s argumenthere is that the Lead Industries decisiondid not address whether Congress had‘‘spoken directly’’ to the precise issueposed by the commenter; that is,whether section 109 must be interpreteddifferently for NAAQS decisionsinvolving non-threshold pollutants and‘‘ambiguous’’ health evidence. The LeadIndustries opinion, which pre-datedChevron, did not pose the question inthose terms. Its focus, however, wasclearly on what Congress intended to bethe basis for NAAQS decisions, in acontext the Court understood to involveconsiderable uncertainty and debateabout the health evidence, as well as thepossibility that there was no threshold

for health effects of the pollutant.55 Inshort, the health evidence was hardly‘‘unambiguous,’’ yet the Courtinterpreted section 109 as precludingconsideration of costs and similarfactors even in allowing a margin ofsafety. Nothing in the Lead Industriesdecision or in the subsequent casessuggests in any way that section 109should be interpreted differently basedon the nature of the pollutants or healthevidence involved, and the Court’sfindings on congressional intent admitof no exceptions:

[T]he statute and its legislative historymake clear that economic considerations playno part in the promulgation of ambient airquality standards under section 109.

647 F.2d at 1148.Alternatively, the commenter argues

that the Lead Industries case decidedthe issue incorrectly in light of theprinciples announced subsequently inChevron. In this context, the commenteressentially argues that the LeadIndustries decision rested on two factorsthat are no longer probative: (1) Thatthere was no indication that Congressmeant to allow consideration of costs inNAAQS decisions, and (2) that Congressspecifically provided for suchconsideration in other sections of theAct but not in section 109. On the firstpoint, the commenter argues that EPA isfree under Chevron to consider costsand similar factors (by reinterpretingsection 109) unless there is evidencethat Congress intended to restrict itsdiscretion. As to the second point, thecommenter argues that similar reasoningwas rejected in Vinyl Chloride.

In Vinyl Chloride, however, an enbanc decision that post-dated Chevron,the Court essentially underscored thepoint that such issues cannot be decidedmechanically but must turn, instead, onmore analytical attention to relevantindicia of congressional intent. See, e.g.,824 F.2d at 1157 n.4; id. at 1157–63.With reference to NAAQS decisions inparticular, the Court concluded thatthere were concrete indications ofcongressional intent to precludeconsideration of costs and similarfactors; for example, the fact that section108 ‘‘enumerate[s] specific factors toconsider and pointedly exclude[s]feasibility.’’ 824 F.2d at 1159. In a latercase, moreover, the same Court held thatEPA could not consider certain factors,in decisions under section 211(f)(4) ofthe Act, for reasons exactly parallel tothose that the commenter criticizes inLead Industries. See Ethyl Corp. v. EPA,51 F.3d 1053, 1057–63 (D.C. Cir. 1995).


56 See 647 F.2d at 1148–51. By contrast, thecommenter’s argument that Congress actuallyintended EPA to consider such factors relies heavilyon (1) statements made in subsequent legislativehistory, most of which were made in floor debate,that sought to justify controversial amendments toestablish a different program than the NAAQS anddid not involve any proposed changes in section109 or related provisions; and (2) statements inearly judicial decisions involving programs underother statutory provisions. In context, EPA believesthese and other statements cited by the commenterare consistent with and do not alter the conclusionthat Congress intended to preclude consideration ofcosts and similar factors under section 109.

57 The commenter argues that the post-Chevroncases accepted the Lead Industries analysisuncritically rather than re-examining it underChevron. Clearly, this elevates form over substance.It is true that neither case referred to Chevron indiscussing the point at issue. In Vinyl Chloride,however, the Court retraced the steps in the LeadIndustries analysis in some detail, characterizedsome of the key evidence reviewed in that analysisin terms going beyond mere rote repetition (e.g., ‘‘afar clearer statement than anything in the presentcase that Congress considered the alternatives’’),and used Chevron-like language in discussing thesignificance of that evidence; that is, that itdemonstrated congressional intention on the pointat issue. E.g., 824 F.2d at 1159. Given that the VinylChloride case was decided 3 years after Chevron,that it was an en banc decision of the D.C. Circuitinvolving interpretation of statutory language verysimilar to that in Lead Industries, and that the Courtcited Chevron twice in analyzing the language andhistory of section 112, it seems highly unlikely thatthe Court was unmindful of Chevron principles inconcluding that Congress intended to precludeconsideration of costs under section 109 but notunder section 112.

In the PM10 decision, the Court confirmed thesharp distinction it had drawn, based on suchevidence of congressional intent, between sections109 and 112 in Vinyl Chloride. 902 F.2d at 972–73. Although discussion of the point was brief anddid not mention Chevron, the industry petitionerraising the point had cited Chevron in arguing thatthe Lead Industries interpretation was not binding,and that EPA’s decision on the PM10 standardsshould be reversed on the ground that it rested ona legal position that EPA unjustifiably believed wasmandated by Congress. Reply Brief of the AmericanIron and Steel Institute at 11 & n.10, NaturalResources Defense Council v. Administrator, 902F.2d 962 (D.C. Cir. 1990) (Nos. 87–1438 et al.).Thus, Chevron issues were properly before theCourt and were brought squarely to its attention.

58 See also 52 FR 24854, July 1, 1987.

59 126 Cong. Rec. 21452, 21455 (1980)(Description of Major Issues and Section-By-SectionAnalysis of Substitute for S. 299).

Beyond this, the commenter’scharacterization of the Lead Industriesdecision ignores or discounts much ofthe key evidence cited by the Court,including the language, structure, andlegislative history of the statutoryscheme established in 1970, for itsconclusion that Congress intended topreclude consideration of costs andsimilar factors in NAAQS decisions.56

As indicated above, the Vinyl Chlorideand PM10 cases, both of which post-dated Chevron, reached the sameconclusion.

Moreover, this series of decisionswent far beyond mere deference to anagency interpretation. As indicated inthe Vinyl Chloride case, the LeadIndustries court found ‘‘clear evidence’’of congressional intent, which was tolimit the factors EPA may considerunder section 109. 824 F.2d 1159.Consistent with Chevron, these findingswere based on traditional tools ofstatutory construction. See id. at 1157–59; Lead Industries, 647 F.2d at 1148–51. In terms of the analytical frameworklater established by Chevron, these wereChevron step one findings, meaning thatthe statute spoke directly to the issueand that the courts, as well as theagency, must give effect to Congress’intent as so ascertained. See 467 U.S. at842–43.57 Thus, absent a more recent

legislative enactment overriding thatintent, EPA has no discretion to alter itslongstanding interpretation thatconsideration of costs and similarfactors is precluded in NAAQSdecisions under section 109.58

As to the commenter’s third keyassertion, Executive Order 12866 (58 FR51735, October 4, 1993) UMRA sections202 and 205, and the RegulatoryFlexibility Act (RFA), as amended bySBREFA, do not conflict with thisinterpretation or require a differentresult. Basically, the commenter arguesthat the Executive Order, UMRA, andthe RFA (as amended by SBREFA)require agencies to use cost (or similarfactors) as a decisional criterion inmaking regulatory decisions, and thatthis modifies the Clean Air Act’sdirective that EPA is precluded fromconsidering costs when setting aNAAQS. The commenter’s argument isflawed on a number of grounds. First,UMRA and the RFA (as amended bySBREFA) do not conflict with section109 because they do not apply to thisdecision, as discussed in Unit VIII ofthis preamble. Second, the ExecutiveOrder and both statutes are quite clearthat they do not override the substantiveprovisions in an authorizing statute.Third, the commenter’s premise thatUMRA and the RFA (as amended bySBREFA) establish substantivedecisional criteria that agencies arerequired to follow is wrong.

As a matter of law, the ExecutiveOrder cannot (and does not purport to)override the Clean Air Act. TheExecutive Order does not conflict withsection 109 because the requirementthat agencies ‘‘select approaches thatmaximize net benefits’’ does not applyif a ‘‘statute requires another regulatoryapproach.’’ EO 12866, sec. (1)(a), 58 FR51735, Oct. 4, 1993. More generally, theExecutive Order provides that agenciesare to adhere to its regulatory principlesonly ‘‘to the extent permitted by law.’’Id., sec. (1)(b).

UMRA sections 202 and 205 do notapply to this decision, as discussed in

Unit VII of this preamble. Even whenthey do apply to a regulatory action,they do not establish decisional criteriathat an agency must follow, much lessoverride decisional criteria establishedin the statute authorizing the regulatoryaction. UMRA does not require anagency to select any particularalternative. Rather, an agency can selectan alternative that is not the least costly,most cost-effective or least burdensomeif the agency explains why, sec.205(b)(1). Such an explanation is notrequired if the least costly, most cost-effective or least burdensome alternativewould have been ‘‘inconsistent withlaw,’’ sec. 205(b)(2), and the onlyalternatives that an agency shouldconsider are ones that ‘‘achieve[] theobjectives of the rule,’’ sec. 205(a). TheUMRA Conference Report confirms thatUMRA does not override theauthorizing statute. ‘‘This section [202]does not require the preparation of anyestimate or analysis if the agency isprohibited by law from considering theestimate or analysis in adopting therule.’’ 141 Cong. Rec. H3063 (daily ed.March 13, 1995).

The RFA (as amended by SBREFA)also does not apply to this decision, asdiscussed in Unit VII of this preamble.As is the case with UMRA, even whenthe RFA (as amended by SBREFA) doesapply to a regulatory action, it does notestablish decisional criteria that anagency must follow, much less overridethe underlying substantive statute.When the RFA was adopted in 1980,Congress made clear that it did not alterthe substantive standards contained inauthorizing statutes: ‘‘The requirementsof section 603 and 604 of this title [toprepare initial and final regulatoryflexibility analyses] do not alter in anymanner standards otherwise applicableby law to agency action.’’ Section 606 ofthe RFA. The legislative history furtherexplains that section 606 ‘‘succinctlystates that this bill does not alter thesubstantive standard contained inunderlying statutes which defines theagency’s mandate.’’59 When Congresspassed SBREFA in 1996 and amendedparts of the RFA, it did not amendsection 606.

Even when a regulatory decision issubject to sections 603 and 604 and anagency is therefore required to analyzealternatives that minimize significanteconomic impacts on small entities, theRFA (as amended by SBREFA) does notestablish decisional criteria that anagency is required to follow. Bothsection 603 and 604 provide that the


alternatives an agency should considerare to be ‘‘consistent with the statedobjectives of applicable statutes.’’ Sec.603 and 604(a)(5). Furthermore,although the RFA (as amended bySBREFA) requires agencies to consideralternatives that minimize impacts onsmall entities subject to the rules’requirements and to explain their choiceof regulatory alternatives, it does notrequire agencies to select suchalternatives. For these reasons, the RFA(as amended by SBREFA) does notconflict with or override the Clean AirAct’s preclusion of considering costsand similar factors in setting NAAQS.

3. Conclusion. In summary, EPAbelieves that the judicial decisions citedabove are both correct and dispositiveon the question of considering costs insetting NAAQS, and that the Agency isnot free to reinterpret the Act on thatquestion.

B. Margin of SafetySeveral commenters questioned the

approach used by the Administrator inspecifying O3 standards that protectpublic health with an adequate marginof safety. Rather than the integrativeapproach applied by the Administrator,these commenters maintained that EPAmust employ a two-step process. Theline of argument was that theAdministrator must first determine a‘‘safe level’’ and then apply a margin ofsafety taking into account costs andsocietal impacts. It was argued that thiswas the only approach that wouldenable the Administrator to reach areasoned decision on a standard levelthat protects public health againstunacceptable risk of harm, such that anyremaining risk was ‘‘acceptable.’’ Ineffect, these commenters argued that theAdministrator must adopt the two-stepmethodology endorsed in VinylChloride, 824 F.2d 1146, for settinghazardous air pollutant standards undersection 112.

In recognition of the complexitiesfacing the Administrator in determininga standard that protects public healthwith an adequate margin of safety, thecourts have declined to impose anyspecific requirements on theAdministrator’s methodologicalapproach. Thus, in Lead Industries thecourt held that the selection of anyparticular approach to providing anadequate margin of safety ‘‘is a policychoice of the type Congress specificallyleft to the Administrator’s judgment.This court must allow him thediscretion to determine which approachwill best fulfill the goals of the Act.’’647 F.2d at 1161–62. As a result, theAdministrator is not limited to anysingle approach to determining an

adequate margin of safety and may, inthe exercise of her judgment, choose anintegrative approach, a two-stepapproach, or perhaps some otherapproach, depending on the particularcircumstances confronting her in agiven NAAQS review.

With respect to the approachadvanced in comment, the PM10 casemade clear that the two-step processendorsed in Vinyl Chloride wasnecessary because of the need undersection 112 of the Act to ‘‘severdeterminations that must be basedsolely on health considerations fromthose that may include economic andtechnical considerations.’’ 902 F.2d at973. Because the Administrator may notconsider cost and technologicalfeasibility under section 109, however,the court concluded that ‘‘the rationalefor parsing the Administrator’sdetermination into two steps isinapposite.’’ Id.

Because such factors as the nature andseverity of the health effects involved,the size of the sensitive population(s) atrisk, the types of health informationavailable, and the kind and degree ofuncertainties that must be addressedwill vary from one pollutant to another,the most appropriate approach toestablishing a NAAQS with an adequatemargin of safety may be different foreach standard under review. Thus, nogeneralized paradigm such as thatimbedded in EPA’s cancer risk policycan substitute for the Administrator’scareful and reasoned assessment of allrelevant health factors in reaching sucha judgment. As noted above, bothCongress and the courts have left to theAdministrator’s discretion the choice ofanalytical approaches and tools,including risk assessments, rather thanprescribing a particular formula forreaching such determinations. Becauseof the inherent uncertainties that theAdministrator must address in marginof safety determinations, they are largelyjudgmental in nature, particularly withrespect to non-threshold pollutants, andmay not be amenable to quantificationin terms of what risk is ‘‘acceptable’’ orany other metric. In view of theseconsiderations, the task of theAdministrator is to select an approachthat best takes into account the healtheffects and other information assessedin the air quality criteria for thepollutant in question and to applyappropriate and reasoned analysis toensure that the scientific uncertaintiesare taken into account in an appropriatemanner.

In this instance, the Administrator hasclearly articulated the factors she hasconsidered, the judgments she has hadto make in the face of uncertain and

incomplete information, and alternativeviews as to how such informationshould be interpreted, in reaching herdecision on standard specifications thatwill protect public health with anadequate margin of safety. See Unit II ofthis preamble. Her conclusions on thesematters are fully supported by therecord.

C. Comment PeriodA number of commenters maintained

that EPA erred by not extending thecomment period for the review of the O3

standards by at least 60 days. Thecommenters further maintained therewas no justification for keeping the O3

standard review on the same scheduleas the PM NAAQS, since the O3 reviewis not subject to a court-ordereddeadline as is PM.

The EPA believes that there arebenefits to reviewing the O3 and PMNAAQS on the same schedule, for thereasons set forth in the proposal, andthat the period available for publiccomment was sufficient. All interestedparties have had ample notice that EPAintended to complete this review of theO3 standards on an expedited basis. TheEPA first announced its intention in aMarch 9, 1993, Federal Register notice(58 FR 13008) when the Administratorannounced her commitment to expeditethe review in light of new scientificevidence of the effects of O3 on humanhealth. In a February 3, 1994, FederalRegister notice (59 FR 5164), theAdministrator announced a schedule forcompletion of the scientific assessmentand review of the standards, includingopportunities for public comment. Thisschedule called for proposal in mid-1996 and a final decision as to whetherto revise the O3 standard by mid–1997.On June 12, 1996, in an advance noticeof proposed rulemaking (61 FR 29719),the Administrator announced herdecision to delay the O3 proposalschedule in order to place it on the sameschedule as the PM standard review. Inthat notice, she explained her rationalefor reviewing the O3 and PM NAAQS onthe same schedule and pointed to thebenefits of developing integratedimplementation strategies. She alsoprovided advance notice of the kinds ofrevisions to the primary and secondaryO3 NAAQS that she was consideringproposing. In effect, the delay of the O3

proposal provided interested parties anadditional 5 months to review EPA’sassessments of the scientific andtechnical information, as well as staffand CASAC recommendations as towhether revisions were appropriate.With this background, EPA believes allinterested parties had ampleopportunity to develop specific


60 This comment period reflects an extension of22 days beyond the 67–day comment periodoriginally announced in the proposal.

comments on the O3 proposal during the89 days allotted for public comment.60

Another commenter raised a morespecific issue in requesting a 60–dayextension of the public comment period.This commenter maintained that suchan extension was necessary becauseEPA did not make publicly availablecertain O3 exposure and health riskassessment reports and an explanatorymemoranda in a timely manner. Inresponse, EPA notes that the documentsin question were entered into the docketon February 12, 1997, and placed on theOAQPS Technology Transfer BulletinBoard on February 13, 1997, so that theywould have wide public circulation.Because this commenter’s organizationwas aware that the reports were underpreparation and had expressed interestin receiving them, copies were sentdirectly to the responsible staff personon February 12, 1997. Given that thesereports build on analyses andmethodologies that were available to thepublic during the scientific phase of theO3 NAAQS review, well in advance ofthe proposal, and that the new analysesand explanatory memorandum wereonly 120 pages in length, EPA believesthat this commenter had sufficient timeto review the material and preparecomments before the close of thecomment period on March 12, 1997.

D. 1990 Act Amendments

Contrary to the view expressed insome public comments, EPA maintainsthat the provisions of subpart 2 of PartD of Title I of the Clean Air Act, enactedin 1990, do not preclude EPA fromrevising the O3 standard. The provisionsof subpart 2 simply do not limit EPA’sclear authority under section 109 torevise the standard.

The basic contention of thecommenters is that because theprovisions of subpart 2 are linked to thecurrent 1–hour, 0.12 ppm O3 standard,they prohibit EPA from revising the O3

standard. These provisions, however, donot lead to such a conclusion. Moreover,the view expressed in these commentsignores provisions indicating thatCongress believed that EPA could revisethe O3 NAAQS.

At the outset, it should be noted thatCongress expressly authorized EPA torevise any ambient air quality standardin section 109. That section, whichrequires EPA to review and revise, asappropriate, each NAAQS every 5 years,contains no language expressly orimplicitly prohibiting EPA from revisinga NAAQS. If Congress had intended to

preclude EPA from reviewing andrevising a NAAQS, which is one ofEPA’s fundamental functions, Congresswould have specifically done so.Clearly, Congress knew how to precludeEPA from exercising otherwise existingregulatory authority and did so in otherinstances. See section202(b)(1)(C)(expressly precluding EPAfrom modifying certain motor vehiclestandards prior to model year 2004);section 112(b)(2)(preventing EPA fromadding to the list of hazardous airpollutants any air pollutants that arelisted under section 108(a) unless theymeet the specific exceptions of section112(b)(2)); section 249(e)(3), (f) andsection 250(b)(limiting EPA’s authorityregarding certain clean-fuel vehicleprograms). No such language wasincluded in either section 109 orelsewhere in the Act and no suchimplication may properly be based onthe provisions of subpart 2 of Part D ofTitle I.

Second, other provisions of the Actexpressly contemplate EPA’s ability torevise any NAAQS, and provide noindication that such ability is limited tostandards other than those whoseimplementation is the subject ofsubparts 2, 3 and 4 of Part D. Forexample, section 110(a)(2)(H)(i)provides that SIPs are to provide forrevisions ‘‘from time to time as may benecessary to take account of revisions ofsuch national primary or secondaryambient air quality standard ***.’’Section 107(d)(1)(A) provides a processfor designating areas as attainment,nonattainment, or unclassifiable ‘‘afterpromulgation of a new or revisedstandard for any pollutant under section109 ***.’’ Section 172(e) addressesmodifications of national primaryambient air quality standards. Finally,section 172(a)(1) expressly contemplatesthat EPA may revise a standard in effectat the time of enactment of the 1990Clean Air Act Amendments. Section172(a)(1)(A) provides EPA withauthority to classify nonattainmentareas on or after the designation of anarea as nonattainment with respect to‘‘any revised standard, including arevision of any standard in effect on thedate of the enactment of the Clean AirAct Amendments of 1990.’’ Plainly,Congress had no intention of prohibitingEPA from revising any of the ambientstandards in effect at the time of theenactment of the 1990 amendments.

Third, the provisions of subpart 2 ofPart D do not support the contentionthat they somehow preclude EPA fromexercising its authority to revise theNAAQS under section 109. The fact thatCongress laid out an implementationprogram for the O3 standard existing at

the time of the 1990 amendments in noway suggests that Congress intended topreclude EPA from exercising theauthority it provided EPA to revise theNAAQS when the health data on whichEPA bases such decisions warranted achange in the standard. Contrary to thiscontention, section 181(a) does notpreclude the designation of areas asnonattainment for O3 that have designvalues less than 0.121 ppm. EPA hasdesignated as nonattainment numerousareas whose design value was less than0.121 ppm, but which violated theexisting 1–hour, 0.12 ppm O3 standard.These areas, referred to as‘‘nonclassifiable nonattainment areas,’’include ‘‘submarginal’’ areas (i.e., O3

nonattainment areas with design valuesbelow 0.121 ppm), (See 57 FR 13498,13524–27, April 16, 1992). These areasinclude areas that were designatednonattainment prior to the 1990amendments and whose nonattainmentdesignation Congress required to becontinued after 1990. See section107(d)(1)(C)(i). Clearly, Congress did notprohibit the designation of areas asnonattainment for O3 with design valuesbelow 0.121 ppm; in fact, in some cases,Congress required it. Furthermore, theposition advanced by the commenterswould mean that, in effect, Congress inthe 1990 amendments legislativelyrevised the then-existing 1–hour, 0.12ppm O3 standard to a 0.121 ppmstandard. There is no indication thatCongress intended to do that.

In addition, the fact that Congressdirected EPA to use ‘‘the interpretationmethodology issued by theAdministrator most recently’’ before thedate of the enactment of the Clean AirAct Amendments of 1990 in the contextof subpart 2 does not add any supportto the commenters’ position; it merelyshows that Congress intended theexisting 1–hour, 0.12 ppm standard tobe implemented in a specified way, notthat Congress intended to preclude EPAfrom using its otherwise applicableauthority to revise the standard.

The EPA also disagrees with thecontention that sections 172(a)(1)(C) and(a)(2)(D), which provide that the generalclassification and attainment dateprovisions of section 172 do not applyto areas for which classifications orattainment dates ‘‘are specificallyprovided under other provisions of thispart,’’ support the conclusion thatCongress intended to prohibit EPA fromrevising the O3 standard. Theseprovisions simply mean that whereCongress elsewhere provided forspecific classifications and attainmentdates, as in the case of subpart 2regarding the 1–hour, 0.12 ppmstandard, EPA is not to modify those


classifications or dates. The EPA is notpurporting to do this. These provisionsdo not lead to the conclusion thatbecause Congress established them forthe O3 standard in effect at the time ofthe 1990 amendments, Congress meantthat EPA could not revise that standardin order to appropriately protect publichealth.

EPA does not accept the thesis thatrevising the O3 standard forces EPA toviolate other provisions of the Act and,therefore, is not an ‘‘appropriate’’revision of the standard under section109. Revising the O3 standard inaccordance with the language of section109 does not result in EPA violating anyprovision of the Act. On the other hand,a determination by EPA that the O3

standard should not be revised, eventhough EPA concludes that it needs tobe revised to protect public health withan adequate margin of safety, wouldviolate section 109.

Also, EPA does not believe thatcarrying out the provisions of section109 to set a new O3 standard to protectpublic health with an adequate marginof safety somehow ‘‘risks underminingboth perceptions and reality of thefunctioning of our democratic form ofgovernment.’’ EPA is merelyimplementing the words of the CleanAir Act, a statute passed by the Congressand signed by the President. To refuseto revise the standard notwithstandingthe need to protect public health asenunciated in section 109 would thwartthe objectives of those who passed andsigned the Clean Air Act on behalf ofthe American public.

Finally, for the reasons stated above,EPA’s analysis of its ability toimplement the revised O3 standardunder the provisions of subpart 1 of PartD of Title I does not support the viewthat Congress prohibited EPA fromrevising the standard. Congress clearlyspecified an approach to theimplementation of the 1–hour, 0.12 ppmO3 standard in the provisions of subpart2 of Part D. EPA believes that the clearand express linkage of that approach tothe 1–hour, 0.12 ppm standard indicatesthat it may implement a revised O3

standard in accord with the generalprinciples of subpart 1 of Part D, asinformed by the no-backslidingprinciple embodied in section 172(e).That Congress directed specifically howEPA and the States should implementthe 1–hour, 0.12 ppm O3 standard doesnot carry with it the implication thatCongress intended to prohibit EPA fromexercising its otherwise clear andexpress authority to revise that standardin order to carry out one of itsfundamental missions, theestablishment of ambient air quality

standards to protect public health withan ample margin of safety. If Congresshad intended to prohibit EPA fromexercising such a fundamental authorityit would have clearly specified (as it didin other instances) that EPA could notdo so.

The EPA also disagrees with thecontention that a revised O3 standardmay not be implemented for so long asthe current 1–hour, 0.12 ppm O3

standard remains in effect. The fact thatthe provisions of subpart 2 of Part D arefocused on the implementation of thecurrent standard does not mean that, ifa new or revised O3 standard ispromulgated pursuant to section 109,the new standard could notsimultaneously be implemented underthe provisions of section 110 andsubpart 1 of Part D, which applyregardless of the criteria pollutant ofconcern. There is no language insections 181 or 182 that precludes theimplementation of a different standardunder other authority; those provisionssimply govern the implementation ofthe 1–hour, 0.12 ppm O3 standard. EPAfurther notes that it has historically hadmore than one primary standard forcriteria pollutants (e.g., annual and 24–hour PM10 and sulfur dioxide standards,and 8–hour and 1–hour CO standards)and believes that had Congress wantedto preclude EPA from implementing twoprimary O3 standards simultaneously itwould have expressly precluded EPAfrom doing so. Thus, EPA does notbelieve that it must repeal the 1–hour,0.12 ppm O3 standard before it canpromulgate and implement a newprimary O3 standard.

V. Technical Changes to Part 50

In the proposal, the EPA proposedtwo alternative secondary standards: (1)A secondary standard set identical tothe proposed 0.08 ppm, 8-hour primarystandard; or (2) a seasonal secondarystandard expressed in the SUM06 form.For the reasons discussed in Unit III, theEPA has decided to promulgate asecondary ambient air quality standardfor O3 that is identical to the primaryambient air quality standard.Accordingly, the language adopted inthe final regulation (40 CFR 50.10) hasbeen revised to reflect this change.

In the proposal, the regulatory text in§ 50.9 inadvertently included languageabout what it means when the standardis not met, that should have beendiscussed in 40 CFR part 50, AppendixH. Therefore this sentence has beenremoved from § 50.10(b), and thediscussion moved to the new AppendixI to 40 CFR part 50, which now providesadditional clarification on calculations

for sites with less than complete data, asdiscussed in Unit VI. of this preamble.

VI. Revisions to Appendices D, E, andH

The EPA is finalizing the changes toAppendices D and E to 40 CFR part 50,that were proposed and described in theproposal. No adverse comments werereceived on these changes.

Because the revocation of the existing1–hour standard will become effectiveat a later date (as discussed above inUnit II.B.4.), EPA is retaining AppendixH in its current form. A new AppendixI explains the computations necessaryfor determining when the new 8–hourprimary and secondary standards aremet.

The new Appendix I addresses datacompleteness requirements, datareporting, handling, and roundingconventions, and example calculations.The discussion in this unit sometimesrefers to the contents of the newAppendix I as revisions to Appendix H,so as to highlight how the newAppendix I differs from the currentAppendix H. For example, the examplecalculations in Appendix I differ fromthose in Appendix H to reflect the finalform of the new 8–hour primarystandard.

In the proposal, two alternativesecondary standards were proposed,and the proposed changes to AppendixH addressed both alternatives: Asecondary standard set identical to theproposed 0.08 ppm, 8–hour primarystandard; or a seasonal secondarystandard expressed in the SUM06 form.For the reasons discussed above, theAdministrator has decided to set thesecondary standard identical to theprimary standard as reflected inAppendix I.

Key elements of Appendix I,particularly as they differ from those ofAppendix H, are outlined below.

A. Data CompletenessOne key change to Appendix H,

incorporated into Appendix I, for thenew 0.08 ppm, 8–hour primary andsecondary standards is that nonumerical adjustment is made to themeasured 8–hour concentrations toaccount for missing or incomplete dataas was the case with the 1–hourstandard. Instead, the EPA has decidedto replace the methodology used toadjust the computation of estimatedexceedances for missing data under the1–hour standard with new datacompleteness requirements for the 8–hour standards.

The EPA proposed that, in order todetermine that the 8–hour standardshave been met at a monitoring site


61 The term precision is used to denote both thereproducibility of a measurement under a constantset of conditions, as well as other components ofmeasurement uncertainty such as instrument driftand relative bias.

during the current 3–year period,revisions to Appendix H would require90 percent data completeness, onaverage, with no single year at the sitehaving less than 75 percent datacompleteness. A site could be found notto have met the standards with less thancomplete data. Almost all commenterssupported deleting the estimatedexceedances missing data adjustmentprocedure of the current 1–hourstandard and replacing it withminimum data completenessrequirements. Several commenters feltthat the proposed data completenessrequirement might be too stringent andwould be difficult to attain. Othercommenters recommended that someconsideration be made for hours lostdue to instrument calibration. A fewcommenters thought that EPA shouldestablish higher minimum datacompleteness requirements.

Based on its analysis of available airquality data, the EPA believes that, withthe changes to the proposal describedbelow, the data completenessrequirement in Appendix I is reasonablegiven that 90 percent of all monitoringsites that currently operate on acontinuous basis meet this objective.The EPA believes that a missing hourduring the day resulting frominstrument calibration should notnegatively impact the ability of amonitoring site to meet the datacompleteness requirements because datacompleteness is based on the number ofdays with valid daily maximum 8–hourconcentrations, not on the number ofnon-missing hours.

In the proposal, the EPA soughtcomment on whether meteorologicaldata could provide an objective basis fordetermining, on a day for which thereis missing data, that the meteorologicalconditions were not conducive to highO3 concentrations, and therefore, thatthe day could be assumed to have an 8–hour daily maximum O3 concentrationless than 0.08 ppm. Under the 0.12 ppm1–hour standard, a missing day isassumed less than the level of thestandard only if the two adjacent daysare non-missing, and the dailymaximum 1–hour concentration on eachof those days is less than or equal to0.09 ppm. In the proposal, the EPAspecifically requested comment on theappropriateness of using data onmeteorological conditions, as well as onother information that would permitbetter definition of those necessaryconditions likely to result in peak 8–hour O3 concentrations in the ranges ofconcern. Most commenters expressingan opinion supported the use ofmeteorological data, as well as ambientdata from nearby monitoring sites to

establish that missing hours could beassumed less than the level of thestandard. Days assumed less than thelevel of the standard would be countedas non-missing when computingwhether the data completenessrequirements have been met at the site.Taking these comments into account,EPA has revised the proposed revisionsto Appendix H, as reflected inAppendix I, to count missing daysassumed less than the standard whencomputing whether the datacompleteness requirement has been met.EPA will develop guidance onmethodologies necessary for usingmeteorological data and ambientmeasurements to make suchdeterminations.

Several commenters expressedconcerns about the possibility thatstratospheric O3 intrusion from aloft orforest fires may lead to exceedances ofthe level of the standard, particularlywithin the context of peak O3

concentrations that have been observedat background sites. Commentersexpressed concern that such eventscould lead to violations of the 8–hourstandard and, therefore, they questionedthe attainability of the proposedstandard. Consistent with a forthcomingupdate to EPA’s policy on naturalevents for the new 8–hour standard,EPA has revised Appendix H tospecifically address this concern bystating that whether to use data affectedby stratospheric O3 intrusion or othernatural events when determining if thestandards have been met is subject tothe approval of the appropriate RegionalAdministrator.

B. Data Handling and RoundingConventions

For the reasons cited above, andtaking into account the advice ofCASAC, the Administrator has set thelevel of the new 8–hour primary andsecondary standards at 0.08 ppm. AsEPA explained in the proposal, the levelof the 8–hour standard is expressed tothe second decimal place, 0.08 ppm,with the support of CASAC and in partto reflect uncertainties in the healtheffects evidence upon which theproposed standard is based. Morespecifically, these uncertainties includethe measurement uncertainty andrepresentativeness inherent in thereported ambient O3 concentrationsused in field and epidemiologicalstudies and the uncertainty in theexposure estimates upon whichquantitative risk assessments have beenbased. In the proposal, EPA stated itsbelief that expressing the proposedstandard to the second decimal place isalso consistent with the quality

assurance guidelines that indicate theprecision61 for such O3 measurementsshall be within ± 15 percent.

To determine whether the standard ismet, EPA proposed that the calculatedvalue of the third-highest maximum 8–hour average concentrations, averagedover 3 years, is compared to the level ofthe standard. It is the level of thestandard, 0.08 ppm, expressed to twodecimal places that determines thenumber of significant digits to be usedwhen comparing air qualitymeasurements to the standard. The EPAproposed that, for hourly data, 8–houraverage O3 concentrations computedfrom such hourly data, and the 3–yearaverages of the third highest maximum8–hour average concentrations, that thethird decimal place is carried forward asthe rounding digit, and the insignificantdigits are truncated. To compare thecalculated 3–year average O3

concentration to the level of thestandard, the third decimal place of thecalculated value is rounded. The currentrounding convention is to round updigits equal to or greater than 5.

In the proposal, EPA recognized thatthe level of public health protectionafforded by the use of the currentrounding convention could be increasedby replacing the current roundingconvention with a convention thatdefined the smallest increment abovethe level of the standard to be 0.001ppm for the purposes of determiningwhether the standard has been met. TheEPA solicited comment on the use ofsuch an alternative roundingconvention, with regard to potentialincreased public health protection, aswell as to potential effects on theprobability of attainmentmisclassifications and on the stability ofthe standard.

Of the many States that commentedspecifically on the rounding convention,most State agencies cited concerns bytheir monitoring staffs about theprecision and accuracy of measured O3

concentrations in ambient environmentsand recommended maintaining thecurrent rounding convention. A tribalassociation also supported the currentrounding convention. Other Stateagencies felt that newer instrumentswere capable of supporting a roundingconvention set at 0.001 ppm. Of thoseenvironmental and health associationsthat commented, all supported replacingthe current rounding convention with


62 One individual commenter provided ananalysis of current monitoring technology andsuggested that the precision and accuracy datasupported setting the standard to three decimalplaces and rounding the annual average third-highest 8–hour average concentration up at 0.001ppm. EPA believes that the precision and accuracydata cited by the commenter does not capture allof the uncertainty inherent in ambient air qualitymeasurements.

the alternative 0.001 ppm convention.62

All industry and trade associations thatcommented on rounding recommendedthat EPA retain the current roundingconvention.

After taking these comments intoaccount, EPA has decided that thecurrent rounding approach isappropriate for comparing monitoringdata to the level of the standardexpressed to two decimal places. Thecurrent rounding procedure has theeffect of reducing the probability ofmisclassifying an attainment area asnonattainment and of producing a morestable attainment test. The EPA believesthat measures that promote a stablecontrol program will lead to greaterlong-term health protection and riskreduction. For the reasons stated above,and taking into account the uncertaintyin the exposure estimates upon whichquantitative risk assessments have beenbased, measurement uncertainty, datarepresentativeness, and the desirabilityof these resulting effects, EPA isretaining the current roundingconvention and finalizing the datahandling and rounding conventions, inAppendix I, as proposed.

VII. Regulatory and EnvironmentalImpact Analyses

As discussed in Unit IV of thispreamble, the Clean Air Act and judicialdecisions make clear that the economicand technological feasibility of attainingambient standards are not to beconsidered in setting NAAQS, althoughsuch factors may be considered in thedevelopment of State plans toimplement the standards. Accordingly,although, as described below, aRegulatory Impact Analysis (RIA) hasbeen prepared, neither the RIA nor theassociated contractor reports have beenconsidered in issuing this final rule.

A. Executive Order 12866Under Executive Order 12866, 58 FR

51735 (October 4, 1993), the Agencymust determine whether a regulatoryaction is ‘‘significant’’ and, therefore,subject to Office of Management andBudget (OMB) review and otherrequirements of the Executive Order.The order defines ‘‘significantregulatory action’’ as any regulatoryaction that is likely to result in a rulethat may:

(1) Have an annual effect on theeconomy of $100 million or more oradversely affect in a material way theeconomy, a sector of the economy,productivity, competition, jobs, theenvironment, public health or safety, orState, local, or tribal governments orcommunities.

(2) Create a serious inconsistency orotherwise interfere with an action takenor planned by another Agency.

(3) Materially alter the budgetaryimpact of entitlements, grants, user fees,or loan programs or the rights andobligations of recipients thereof.

(4) Raise novel legal or policy issuesarising out of legal mandates, thePresident’s priorities, or the principlesset forth in the Executive Order.

In view of its important policyimplications, this action has beenjudged to be a ‘‘significant regulatoryaction’’ within the meaning of theExecutive Order. As a result, undersection 6 of the Executive Order, EPAhas prepared an RIA, entitled‘‘Regulatory Impact Analysis forParticulate Matter and Ozone NationalAmbient Air Quality Standards andProposed Regional Haze Rule (July1997).’’ This RIA assesses the costs,economic impacts, and benefitsassociated with potential Stateimplementation strategies for attainingthe PM and O3 NAAQS and theproposed Regional Haze Rule. Changesmade in response to OMB suggestions orrecommendations will be documentedin the public docket and made availablefor public inspection at EPA’s Air andRadiation Docket Information Center(Docket No. A-95-58). The RIA will bepublicly available in hard copy bycontacting the U.S. EnvironmentalProtection Agency Library at the addressunder ‘‘Availability of RelatedInformation’’ and in electronic form asdiscussed above in ‘‘ElectronicAvailability.’’

B. Regulatory Flexibility AnalysisThe Regulatory Flexibility Act (RFA),

5 U.S.C. 601 et seq., provides that,whenever an agency is required topublish a general notice of rulemakingfor a proposed rule, the agency mustprepare an initial regulatory flexibilityanalysis for the proposed rule unless thehead of the agency certifies that the rule‘‘will not, if promulgated, have asignificant economic impact on asubstantial number of small entities’’(section 605(b)). The EPA certified eachof the proposed NAAQS rules based onits conclusion that the rule would notestablish requirements applicable tosmall entities and therefore would nothave a significant economic impact onsmall entities within the meaning of the

RFA. See 61 FR 65638, 65668 (PMproposal); 61 FR 65716, 65746 (ozoneproposal), both published on December13, 1996. Accordingly, the Agency didnot prepare an initial regulatoryflexibility analysis for the proposedrule, but it did conduct a more generalanalysis of the potential impact on smallentities of possible State strategies forimplementing any new or revisedNAAQS.

At the heart of EPA’s certification ofthe proposed NAAQS rule was theAgency’s interpretation of the word‘‘impact’’ as used in the RFA. Is the‘‘impact’’ to be analyzed under the RFAa rule’s impact on the small entities thatwill be subject to the rule’srequirements, or the rule’s impact onsmall entities in general, whether or notthey will be subject to the rule? In thecase of NAAQS rules, the questionarises because of the congressionally-designed mixture of Federal and Stateresponsibilities in setting andimplementing the NAAQS.

As EPA explained in the proposal,NAAQS rules establish air qualitystandards that States are primarilyresponsible for meeting. Under section110 and part D of Title I of the CAA,every State develops a StateImplementation Plan (SIP) containingthe control measures that will achieve anewly promulgated NAAQS. States havebroad discretion in the choice of controlmeasures. As the U.S. Supreme Courtnoted in Train v. NRDC:

[P]rimary [NAAQS] deal with the quality ofoutdoor air and are fixed on a nationwidebasis at a level which the agency determineswill protect the public health. It is theattainment and maintenance of thesestandards which section 110(a)(2)(A) requiresthat State plans provide. In complying withthis requirement, a State’s plan must include‘‘emission limitations’’ which are regulationsof the composition of substances emitted intothe ambient air from such sources as powerplants, service stations and the like. They arethe specific rules to which operators ofpollution sources are subject and which, ifenforced, should result in ambient air whichmeets the national standards.

The Agency is plainly charged by the Actwith the responsibility for setting thenational ambient air standards. Just asplainly, it is relegated to a secondary role inthe process of determining and enforcing thespecific, source-by-source emissionlimitations which are necessary if thenational standards are to be met. Under110(a)(2), the Agency is required to approvea State plan which provides for the timelyattainment and maintenance of the ambientair standards, and which also satisfies thatsection’s other general requirements. The Actgives the agency no authority to question thewisdom of a State’s choices of emissionlimitations if they are part of a plan whichsatisfies the standards of 110(a)(2) and theAgency may devise and promulgate a plan of


63 It is worth noting that Federal rules that applynationally also play a role in reducing emissionsgoverned by NAAQS. For instance, EPA rules underTitle II of the CAA require reductions in ozone-forming emissions from on and off-road vehiclesand the fuels that power them. When EPA issuessuch rules, it conducts the analysis required underthe RFA. For example, EPA performed regulatoryflexibility analyses for the reformulated gasolinerule issued under section 211(k) of the CAA. See59 FR 7716, February 16, 1994.

its own only if the state fails to submit animplementation plan which satisfies thosestandards. Section 110(c).

421 U.S. 60, at 78–79 (1975) (emphasisin original). In short, NAAQS rulesthemselves do not establish any controlrequirements applicable to smallentities. State rules implementing theNAAQS may establish suchrequirements and the extent to whichthey do depends primarily on eachState’s strategy for meeting theNAAQS.63

To determine the properinterpretation of ‘‘impact’’ under theRFA, EPA considered the RFA’s statedpurpose, its requirements for regulatoryflexibility analyses, its legislativehistory, the amendments made by theSmall Business Regulatory EnforcementFairness Act of 1996 (SBREFA)(Pub. L.104–121), and caselaw. The EPAconcluded that all of these traditionaltools of statutory construction point inone direction—that an agency isrequired to assess the impact of a ruleon the small entities that will be subjectto the rule’s requirements, because thepurpose of a regulatory flexibilityanalysis is to consider ways of easing oreven waiving a rule’s requirements asthey will apply to small entities,consistent with the statute authorizingthe rule. That purpose cannot be servedin the case of the rules like the NAAQSthat do not have requirements thatapply to small entities.

More specifically, EPA noted that itsinterpretation of ‘‘impact’’ flows fromthe express purpose of the RFA itself.As the RFA’s ‘‘Findings and Purposes’’section (Pub. L. 96–354, section 2)makes clear, Congress enacted the RFAin 1980 out of concern that agencieswere writing one-size-fits-all regulationsthat in fact did not fit the size andresources of small entities. Congressnoted that it is generally easier for bigbusinesses to comply with regulations,and that small businesses are thereforeat a competitive disadvantage incomplying with uniform rules. Congressalso noted that small entities’ relativecontribution to the problem a rule issupposed to solve may not warrantapplying the same requirements to largeand small entities alike. In the RFAitself, Congress therefore stated:

It is the purpose of this Act to establish asa principle of regulatory issuance thatagencies shall endeavor, consistent with theobjectives of the rule and of applicablestatutes, to fit regulatory and informationalrequirements to the scale of the businesses,organizations, and governmentaljurisdictions subject to regulation.

[Pub. L. 96–354, section 2(b).]The EPA further noted that the RFA

sections governing initial and finalregulatory flexibility analyses reflectthis statement of purpose. RFA sections603 and 604 require that initial and finalregulatory flexibility analyses identifythe types and estimate the numbers ofsmall entities ‘‘to which the proposedrule will apply’’ (sections 603(b)(3) and604(a)(3)). Similarly, they require adescription of the ‘‘projected reporting,recordkeeping and other compliancerequirements of the proposed rule,including an estimate of the classes ofsmall entities which will be subject tothe requirement’’ (sections 603(b)(4) and604(a)(4)). At the core of the analyses isthe requirement that agencies identifyand consider ‘‘significant regulatoryalternatives’’ that would ‘‘accomplishthe stated objectives of applicablestatutes and which minimize anysignificant economic impact of theproposed rule on small entities’’(section 603(c) and 604(a)(5)). Amongthe types of alternatives agencies are toconsider are the establishment ofdifferent ‘‘compliance or reportingrequirements or timetables’’ for smallentities and the exemption of smallentities ‘‘from coverage of the rule, orany part’’ of the rule (section 603(c)(1)and (4)). The RFA thus makes clear thatregulatory flexibility analyses are tofocus on how to minimize rulerequirements on small entities.

As EPA further explained, sinceregulatory flexibility analyses are notrequired for a rule that will not have a‘‘significant economic impact on asubstantial number of small entities,’’ itmakes sense to interpret ‘‘impact’’ inlight of the requirements for suchanalyses. Regulatory flexibility analyses,as described above, are to consider howa rule will apply to small entities andhow its requirements may be minimizedwith respect to small entities. In thiscontext, ‘‘impact’’ is appropriatelyinterpreted to mean the impact of a ruleon the small entities subject to the rule’srequirements.

The Agency cited two Federal courtcases in support of its interpretation. InMid-Tex Elec. Co-op v. FERC, 773 F.2d327, 342 (D.C. Cir. 1985), petitionersclaimed that the RFA required anagency to analyze the effects of a rule onsmall entities that were not regulated bythe rule but might be indirectly

impacted by it. Petitioners noted thatthe Small Business Administration(SBA) also interpreted the RFA torequire analysis of a rule’s impact onsmall entities not regulated by the rule,and argued that the court should deferto the SBA’s position in light of itscompliance monitoring role under theRFA. After reviewing the RFA’s‘‘Findings and Purposes’’ section, itslegislative history, and its requirementsfor regulatory flexibility analyses, theMid-Tex court rejected petitioners’interpretation. As the court explained:

The problem Congress stated it discernedwas the high cost to small entities ofcompliance with uniform regulations, andthe remedy Congress fashioned—carefulconsideration of those costs in regulatoryflexibility analyses—is accordingly limited tosmall entities subject to the proposedregulation. *** [W]e conclude that an agencymay properly certify that no regulatoryflexibility analysis is necessary when itdetermines that the rule will not have asignificant economic impact on a substantialnumber of small entities that are subject tothe requirements of the rule.

Id. at 342. Notably, Congress let thisinterpretation stand when it recentlyamended the RFA in enacting theSBREFA.

The EPA also cited a recent caseaffirming the Mid-Tex court’sinterpretation. In United DistributionCompanies v. FERC, 88 F.3d 1105, 1170(D.C. Cir. 1996), the court noted that theMid-Tex court:

*** conducted an extensive analysis of theRFA provisions governing when a regulatoryflexibility analysis is required and concludedthat no analysis is necessary when an agencydetermines ‘‘that the rule will not have asignificant economic impact on a substantialnumber of small entities that are subject tothe requirements of the rule’’.

Id., citing and quoting Mid-Tex(emphasis added by United Distributioncourt).

The Agency went on to explain thatgiven the Federal/State partnership forattaining healthy air, the proposedNAAQS, if adopted, would not establishany requirements applicable to smallentities. Instead, any new or revisedstandard would establish levels of airquality that States would be primarilyresponsible for achieving by adoptingplans containing specific controlmeasures for that purpose. Theproposed NAAQS rule was thus notsusceptible to regulatory flexibilityanalysis as prescribed by the amendedRFA. Since it would establish norequirements applicable to smallentities, it afforded no opportunity forEPA to fashion for small entities lessburdensome compliance or reportingrequirements or timetables, or


exemptions from all or part of the rule.For these reasons, EPA certified that theproposed rule ‘‘will not, if promulgated,have a significant economic impact ona substantial number of small entities,’’within the meaning of the RFA. BecauseEPA was not required to prepare aninitial regulatory flexibility analysis forthe rule, it was also not required toconvene a Small Business AdvocacyReview Panel for the rule under RFAsection 609(b) as added by SBREFA.

Notwithstanding its certification ofthe proposed rule, EPA recognized thatthe proposed NAAQS, if adopted,would begin a process of Stateimplementation that could eventuallylead to small entities having to complywith new or different control measures,depending on the implementation plansdeveloped by the States. EPA alsorecognized that the CAA does not allowEPA to dictate or second-guess howStates should exercise their discretionin regulating to attain any new orrevised NAAQS. Under thosecircumstances, EPA concluded that thebest way to take account of small entityconcerns regarding any new or revisedNAAQS was to work with small entityrepresentatives and States to provideinformation and guidance on how Statescould address small entity concernswhen they write their implementationplans.

In line with this approach, as part ofthe RIA it prepared for the proposedNAAQS, EPA analyzed howhypothetical State plans forimplementing the proposed rule mightaffect small entities. The analysis wasnecessarily speculative and limited,since it depended on projections aboutwhat States might do several years inthe future and did not take into accountany new strategies that might bedeveloped and recommended by theFACA subcommittee formed to helpdevise potential strategies forimplementing a new or revised NAAQS(see discussion of RIA and FACAprocess in the previous Unit of thisnotice). Nevertheless, the analysisprovided as much information onpotential small entity impacts as wasreasonably available at the time of theproposed rule.

The Agency also took steps to ensurethat small entities’ voices were heard inthe NAAQS rulemaking itself. With JereGlover, Chief Counsel for Advocacy ofthe SBA, EPA convened outreachmeetings modeled on the SBREFA panelprocess to solicit and convey smallentities’ concerns with the proposedNAAQS. Two meetings were held aspart of that process, on January 7 andFebruary 28, 1997, with a totalattendance of 41 representatives of

small businesses, small governmentsand small nonprofit organizations. Bothmeetings were attended byrepresentatives of SBA and the Office ofManagement and Budget, as well as ofEPA. The key concerns raised by smallentities at those meetings related to thescientific foundation of the proposedNAAQS and the potential cost ofimplementing it, the same concernsraised by other industry commenters onthe proposed rule. The Agencyproduced a report on the meetings toensure that small entity concerns werepart of the rulemaking record when EPAmade its final decision on the proposal.

In light of States’ pivotal role inNAAQS implementation, EPA alsoundertook a number of additionalactivities to assist and encourage theStates to be sensitive to small entityimpacts as they implement any new orrevised NAAQS. With the SBA, EPAbegan an interagency panel process tocollect advice and recommendationsfrom small entity representatives onhow States could lessen any impacts onsmall entities. The EPA plans to issuematerials in two phases to help Statesdevelop their implementation plans. Inview of States’ discretion inimplementing the NAAQS, thesematerials will mostly take the form ofguidance, which is not subject to theRFA’s requirement for initial regulatoryflexibility analysis. (Under RFA section603, that requirement applies only tobinding rules that are required toundergo notice-and-commentrulemaking procedures.) But regardlessof the form such materials take, EPA isemploying panel procedures to ensurethat small entities have an opportunityto raise any concerns prior to thematerials being issued in draft form.

To supplement the input the Agencyreceives from the ongoing CAAACprocess (described earlier in this Unit ofthis preamble), EPA also added moresmall entity representatives to thesubcommittee on implementation of anynew or revised NAAQS. Theserepresentatives have formed a smallentity caucus to develop and bring tothe subcommittee a focused approach tosmall entity issues. These newsubcommittee members are also part ofthe group in the aforementioned panelprocess. By means of these variousprocesses, EPA hopes to promote theconsideration of small entity concernsand advice throughout the NAAQSimplementation process.

In response to the proposed rule, anumber of commenters questionedEPA’s decision to certify that theproposed NAAQS will not have asignificant impact on a substantialnumber of small entities. Some

commenters disagreed with EPA’s viewthat the proposed NAAQS would notestablish regulatory requirementsapplicable to small entities. Thesecommenters argued that a number ofcontrol requirements applicable to smallentities would automatically result frompromulgation of the proposed NAAQS,such as new reasonable further progress,SIP and Federal Implementation Plan(FIP) requirements. Other commentersstated that it is possible for EPA toassess the impacts of the NAAQSrevision on small entities and that, to alimited extent, EPA has already done so.Further, a number of commentersargued that EPA has a legal obligationunder the RFA, as amended by SBREFA,to choose a NAAQS alternative thatminimizes the impact on small entities.Some commenters questioned EPA’sinterpretations of the Mid-Tex andUnited Distribution cases. In addition,other commenters stated that EPA’sposition regarding the NAAQS and theRFA is inconsistent with its pastpractice and the legislative history ofthe RFA. Finally, a few commentersnoted that the panel process EPAconducted for the proposed NAAQS didnot satisfy the requirements of SBREFA.

EPA disagrees that promulgation ofthe NAAQS will automatically result incontrol requirements applicable to smallentities that EPA can and must analyzeunder the RFA. As noted previously, aNAAQS rule only establishes a standardof air quality that other CAA provisionscall on States (or in case of Stateinaction, the Federal government) toachieve by adopting implementationplans containing specific controlmeasures for that purpose. Followingpromulgation of a new or revisedNAAQS, section 110 of the CAArequires States and EPA to engage in adesignation process to determine whatareas within each State’s borders areattaining or not attaining the NAAQS.Under section 110 and parts C and D ofTitle I of the CAA, States then conducta planning process to develop and adopttheir SIPs. Depending on an area’sdesignation for the particular NAAQS,these and other Title I provisionsrequire a State’s SIP to contain certaincontrol programs in addition to thecontrol measures that the State decidesare also needed to attain and maintainthe NAAQS.

The fact that the CAA requires SIPs tocontain certain control programs undercertain circumstances does not meanthat EPA either can or must conduct aregulatory flexibility analysis of a ruleestablishing a NAAQS. Just from thestandpoint of feasibility, EPA cannotknow which areas will be subject towhat mandatory SIP programs until


64 Contrary to what some commenters assumed,the SIP requirements of subpart 2 of part D of TitleI will not apply to SIPs to implement the revisedozone NAAQS. Those requirements were enactedby Congress in 1990 to address nonattainment of a0.12 ppm 1-hour ozone NAAQS. To the extent thoserequirements remain in effect, they apply only toSIPs for areas still in nonattainment with thatstandard; they do not apply to SIPs for areas innonattainment only with respect to the ozoneNAAQS adopted today. Further, to the extent SIPsfor areas in nonattainment with the previous ozonestandard remain subject to subpart 2 requirements,there will be no incremental change in the impacton sources regulated by the States’ SIPs pursuantto the requirements as a result of today’spromulgation.

65 If and when the Agency issues any rulesaddressing State implementation of any statutorilyrequired actions, EPA would analyze and addressthe impact of those rules on small entities asappropriate under the RFA.

after the designation process iscompleted. Beyond that, any mandatorySIP programs are still implemented bythe States, and States have considerablediscretion in how they implement them.For instance, the reasonable furtherprogress requirement under section 172leaves States broad discretion todetermine the rate of progress and thecontrol measures to achieve thatprogress.64 As a result, EPA cannot becertain where and how any mandatoryprograms will be implemented withrespect to small (or large) entities. Muchless can EPA know about how Stateswill exercise their discretion to developadditional controls needed to attain andmaintain the NAAQS.

Even if EPA could know exactly howany mandatory SIP programs wouldapply to small entities, the purpose ofthe RFA is not served by attempting aregulatory flexibility analysis of Stateimplementation of those programs. Asexplained previously, the RFA and thecaselaw interpreting it clearly establishthat the purpose of the RFA is topromote Federal agency efforts to tailora rule’s requirements to the scale of thesmall entities that will be subject to it.That purpose cannot be served in thecase of a NAAQS rule since the ruledoes not establish requirementsapplicable to small entities. Inpromulgating a NAAQS, the only choicebefore EPA concerns the level of thestandard, not its implementation. Whilemandatory SIP programs may ultimatelyfollow from promulgation of theNAAQS, there is nothing EPA can do insetting the NAAQS to tailor thoseprograms as they apply to small entities.Whether and how the programs willapply in particular nonattainment areasis beyond the scope of the NAAQSrulemaking and, indeed, beyond EPA’sreach in any rulemaking to the extentthe applicability and terms of theprograms are prescribed by statute.65

Moreover, any mandatory SIP programs

are supplemented by discretionary Statecontrols that EPA has no power to tailorunder the RFA or the CAA (see Train v.NRDC, quoted previously).

The commenters’ suggestions forminimizing the potential impact of theNAAQS rule on small entities run afoulof both the RFA and the CAA. Somesuggested that EPA set a less stringentstandard (or no standard at all in thecase of PM2.5) to reduce the chance thatsmall entities would become subject tonew or tighter SIP requirements. Otherssuggested that EPA require States toexempt small entities from new ortighter SIP requirements. However, asexplained in a previous Unit of thisnotice addressing the Agency’sauthority to consider factors other thanpublic health in setting primaryNAAQS, the RFA neither requires norauthorizes EPA to set a less stringentNAAQS than the applicable CAAprovisions allow in order to reducepotential small entity impacts. Indeed,the RFA provides that any means ofproviding regulatory flexibility to smallentities be consistent with the statuteauthorizing the rule. Moreover, even ifEPA set a less stringent standard, Statescould still exercise their discretion toobtain any needed emission reductionsfrom small entities. As the SupremeCourt in Train v. NRDC made clear, EPAhas no authority to forbid States fromobtaining reductions from any particularcategory of stationary sources, includingsmall entities. See also, Virginia v. EPA,No. 108 F.3d 1397, 1408 (D.C. Cir.1997), quoting Union Electric v. EPA,427 U.S. 246, 269 (1976) (‘‘section 110left to the states the power to determinewhich sources would be burdened byregulations and to what extent’’).

EPA’s approval of SIPs for the new orrevised NAAQS also will not establishnew requirements, but will insteadsimply approve requirements that aState is already imposing. And again,EPA does not have authority todisapprove a State’s plan except to theextent that the plan fails to demonstrateattainment and maintenance of theNAAQS as required by Title I of theCAA. In cases where EPA promulgatesa FIP, EPA might establish controlrequirements applicable to smallentities, and in such a circumstance,EPA would conduct the analysesrequired by the RFA.

Some commenters argued that underthe RFA as amended by SBREFA, EPAnow has an obligation to choose thealternative that minimizes the impact onsmall entities when setting the NAAQS.As indicated above, EPA disagrees withthe commenters’ argument for thereasons stated in the Unit of this noticediscussing the Agency’s authority to

consider costs and other factors notrelated to public health in setting andrevising primary NAAQS. In a nutshell,both the text and legislative history ofthe RFA make clear that the RFA doesnot override the substantive provisionsof the statute authorizing the rule, butonly requires agencies to identify andconsider ways of minimizing theeconomic impact on small entitiessubject to the rule in a mannerconsistent with the authorizing statute.

Some commenters disagreed withEPA’s interpretation of the Mid-Tex andUnited Distribution cases. In particular,these commenters noted that in thosecases the relevant regulatory agency,FERC, wholly lacked jurisdiction toregulate the small entities at issue.According to these commenters, EPAdoes have the ability and jurisdiction toregulate small entities in the case of theNAAQS, and therefore EPA’s relianceon Mid-Tex and United Distribution ismisplaced.

The commenters’ attempt todistinguish the FERC cases from theNAAQS rulemaking wholly overlooksthe courts’ reasoning, which in fact fullysupports EPA’s certification of theproposed NAAQS. As described above,the Mid-Tex court exhaustivelyreviewed the relevant sections of theRFA and its legislative history. Itsanalysis revealed that Congress passedthe RFA out of concern with one-size-fits-all regulations and fashioned aremedy limited to regulations that applyto small entities. This principle is fullyapplicable to the NAAQS, which createsno rule requirements that apply to smallentities.

The fact that FERC had no regulatoryauthority over the small entitiesindirectly affected by its rules played noessential role in the court’s rationale.FERC could (and apparently did in theMid-Tex rulemaking) estimate thepotential indirect impact of its rules onsmall entities. Presumably, FERC couldhave also mitigated any indirect impactby changing some aspect of the rule (orelse the small entities would have hadno incentive to sue the agency). Thecourt nevertheless found it unnecessaryfor FERC to do either, based on itsreading of the RFA as limited to analysisof a rule’s impact on the small entitiessubject to the rule’s requirements. Inreaching its decision, the court notedthat requiring agencies to ‘‘considerevery indirect effect that any regulationmight have on small businesses *** isa very broad and ambitious agenda, ***that Congress is unlikely to haveembarked on *** without airing thematter.’’ Mid-Tex, 773 F.d. at 343.

The commenters also overstate EPA’sregulatory authority over small entities


66 As commenters pointed out, the RIA for theproposed PM NAAQS does state that ‘‘[t]hescreening analysis *** provides enough informationfor an initial regulatory flexibility analysis (RFA) ifsuch an analysis were to be done.’’ That statementwas mistaken and was not made in the RIA for theproposed ozone NAAQS. While both RIAsattempted to gauge the potential impact on smallentities of State implementation of the proposedNAAQS, neither could or did identify any specificcontrol or information requirements contained inthe NAAQS rule that would apply to small entities.Indeed, both RIAs made clear that the impact beinganalyzed was that of potential State measures toattain the NAAQS, and that such an analysis wasinherently speculative and uncertain. Thus, theRIAs actually confirm EPA’s statement in thepreambles for the proposed NAAQS thatconducting a complete regulatory flexibilityanalysis is not feasible for rules setting or revisinga NAAQS.

with respect to the regulation of criteriapollutants. Various CAA provisionsauthorize EPA to regulate various typesof sources at the Federal level toaccomplish specified goals. However,EPA’s authority to more generallyregulate sources, including smallentities, in the manner of SIPs is limitedto instances of State default of SIPresponsibilities. When that occurs, EPAmay issue a FIP containing specificcontrol measures, and to the extent aproposed FIP would establish controlmeasures applicable to small entities,EPA would analyze the small entityimpact of those measures as required bythe RFA. In 1994, for example, EPAprepared an initial regulatory flexibilityanalysis when it proposed a FIP for LosAngeles. See 59 FR 23264, May 5, 1994.

As noted above, Congress let the Mid-Tex interpretation stand when itrecently amended the RFA in enactingSBREFA. If it had disagreed with thecourt’s decision, it would have revisedthe relevant statutory provisions orotherwise indicated its disagreementwhen it enacted SBREFA. Instead,Congress actually reinforced the Mid-Tex court’s interpretation of the RFA inenacting section 212(a) of SBREFA. Thatsection requires that an agency issue a‘‘small entity compliance guide’’ for‘‘each rule *** for which an agency isrequired to prepare a final regulatoryflexibility analysis under section 604’’of the RFA. The guide is ‘‘to assist smallentities in complying with the rule’’ by‘‘explain[ing] the actions a small entityis required to take to comply’’ with therule (SBREFA section 212(a)).Obviously, it makes no sense to preparea small entity compliance guide for arule that does not apply to smallentities. SBREFA thus stands as furtherconfirmation that Congress intendedregulatory flexibility analyses to addressonly rules that establish requirementssmall entities must meet. SinceSBREFA’s passage, the UnitedDistribution court has affirmed the Mid-Tex court’s interpretation.

Some commenters noted that EPA’sinformal panel process did not complywith the requirements of SBREFA. TheEPA did not convene a SBREFA panelbecause such a panel is not required forrules like the NAAQS that do not applyto small entities. Under the RFA asamended by SBREFA, since the Agencycertified the proposal, it was notrequired to convene a panel for it.Nevertheless, EPA conducted thevoluntary panel process describedabove, as well as other voluntary smallbusiness outreach efforts. The processcould not comply with the analyticalrequirements of the RFA for the reasonsgiven above. However, it could and did

ensure that EPA heard directly fromsmall entities about the NAAQSproposals.

A few commenters stated that EPA’sview of the NAAQS and the RFA isinconsistent with EPA’s past positionsregarding the RFA and NAAQSrevisions. Some commenters also citedthe Regulatory Impact Analysis for theproposed NAAQS and noted that thisanalysis demonstrates EPA’s ability toestimate the impact of the NAAQS onsmall entities, thereby undercuttingEPA’s argument that it is not able toperform a regulatory flexibility analysiswhen setting the NAAQS.

Past Federal Register notices makeclear that the nature of the NAAQSmakes a regulatory flexibility analysisinapplicable to NAAQS rulemakings.For instance, in 1984, EPA stated that a‘‘NAAQS for NOx by itself has no directimpact on small entities. However, itforces each State to design andimplement control strategies for areasnot in attainment.’’ 49 FR 6866, 6876,February 23, 1984; see also, 50 FR37484, 37499, September 13, 1985; 50FR 25532, 25542, June 19, 1985(NAAQS for NO2 do not impact smallentities directly). EPA stated again in1987 that the NAAQS ‘‘themselves donot contain emission limits or otherpollution controls. Rather, such controlsare contained in State implementationplans.’’ 52 FR 24634, 24654, July 1,1987.

EPA has typically performed ananalysis to assess, to the extentpracticable, the potential impact ofretaining or revising the NAAQS onsmall entities, depending on possibleState strategies for implementing theNAAQS. These analyses have providedas much insight into the potential smallentity impacts of implementing revisedNAAQS as could be provided at theNAAQS rulemaking stage. In someinstances, these preliminary ‘‘analyses’’were described as ‘‘regulatory flexibilityanalys[es]’’ or as analyses ‘‘pursuant tothis [Regulatory Flexibility] Act.’’ See,e.g., 52 FR 24634, 24654, July 1, 1987;50 FR 37484, 37499, September 13,1985.

However, these analyses were basedon hypothetical State control strategies,and EPA made the point on variousoccasions that any conclusions to bedrawn from such analyses were‘‘speculative,’’ given that the NAAQSthemselves do not impose requirementson small entities. Although these pastanalyses reflected the Agency’s bestefforts to evaluate potential impacts,they were not regulatory flexibilityanalyses containing the necessaryelements required by the RFA. Theseanalyses, for example, did not describe

the ‘‘reporting, recordkeeping and othercompliance requirements’’ of theproposed NAAQS rules that wouldapply to small entities, since theNAAQS rules did not apply to smallentities. Nor did they determine howthe proposed NAAQS rules could beeased or waived for small entities. Suchan analysis is not possible in the case ofthe NAAQS. To the extent EPA labeledthese analyses regulatory flexibilityanalyses in the past, that label wasinappropriate. EPA’s current practice isto describe such an analysis moreaccurately as a ‘‘general analysis of thepotential cost impacts on smallentities.’’ See, e.g., 61 FR 65638, 65669,65747, December 13, 1996 (current O3

and PM NAAQS proposals).66 EPA’sanalytical approach to small entityimpacts of the NAAQS has thusremained consistent over time.

One commenter noted that thelegislative history of the RFA suggeststhat the RFA was intended to apply tothe NAAQS. As noted previously, EPA’sreading of both the RFA and SBREFA,based on the language of the statute asamended and its legislative historiesand applicable caselaw, is that the RFArequirements at issue do not apply tothe NAAQS. The legislative historycited by the commenter does not changethis conclusion.

In fact, the statement by SenatorCulver on which the commenter reliesdoes not indicate that the NAAQSshould be subject to regulatoryflexibility analyses. Rather, SenatorCulver uses the NAAQS as an exampleof the type of standard that agencieswould not change as a result of theRegulatory Flexibility Act. According toSenator Culver, Section 606 ‘‘succinctlystates that this bill does not alter thesubstantive standard contained inunderlying statutes which defines theagency’s mandate.’’ 126 Cong. Rec. S21455 (Aug. 6, 1980) daily ed. Afterciting CAA section 109, Senator Culvergoes on to describe EPA’s bubble policy


67 As noted in Unit VII.B. of this preamble, aNAAQS rule only establishes a standard of air

quality that other provisions of the Act call onStates (or in the case of State inaction, the Federalgovernment) to achieve by adoptingimplementation plans containing specific controlmeasures for the purpose. Thus, it is questionablewhether the NAAQS itself imposes an enforceableduty and thus whether it is a significant Federalmandate within the meaning of UMRA. EPA neednot and does not reach this issue today. For thereasons given in this unit, even if the NAAQS weredetermined to be a significant Federal mandate,EPA does not have any obligations under sections202 and 205 of UMRA, and EPA has met anyobligations it would have under section 204 ofUMRA.

68 In addition to the estimates and assessmentsdescribed in section 202 of UMRA, writtenstatements are also to include an identification ofthe Federal law under which the rule ispromulgated (section 202(a)(1) of UMRA) and adescription of outreach efforts under section 204 ofUMRA (section 202(a)(5) of UMRA). Although theserequirements do not apply here because a writtenstatement is not required under section 202 ofUMRA, this preamble identifies the Federal lawunder which this rule is being promulgated and awritten statement describing EPA’s outreach effortswith State, local, and tribal governments will beplaced in the docket.

(which addresses the limits onemissions from a particular facility) asthe type of flexible regulation thatagencies should consider, once EPA hasset a NAAQS. ‘‘The important point forpurposes of this discussion is that the‘bubble concept’, a type of flexibleregulation, in no manner altered thebasic statutory substantive standard ofthe EPA *** . No regulatory flexibilityanalysis alters the substantive standardotherwise applicable by law to agencyaction.’’ Id. Thus, contrary to thesuggestion of the commenter, SenatorCulver’s statement actually confirmsthat the time to consider regulatoryflexibility is when regulationsapplicable to sources are beingestablished, not when a NAAQS itself isbeing set.

Under section 604 of the RFA,whenever an agency promulgates a finalrule under section 553 of theAdministrative Procedure Act, afterbeing required by that section or anyother law to publish a general notice ofproposed rulemaking (NPRM), theagency is required to prepare a finalregulatory flexibility analysis. RFAsection 605(b) provides, however, thatsection 603 (re initial regulatoryflexibility analyses) and section 604 donot apply if the agency certifies that therule will not have a significanteconomic impact on a substantialnumber of small entities and publishessuch certification at the time ofpublication of the NPRM or at the timeof the final rule.

As noted above, EPA certified today’srule at the time of the NPRM. Afterconsidering the public comments on thecertification, EPA continues to believethat today’s rule will not have asignificant economic impact on asubstantial number of small entities forthe reasons explained above and that ittherefore appropriately certified therule. Further, as required by the CAA,EPA is promulgating today’s rule underCAA section 307(d). For all theforegoing reasons, EPA has not prepareda final regulatory flexibility analysis forthe rule. The Agency has nonethelessanalyzed in the final RIA for the rule thepotential impact on small entities ofhypothetical State plans forimplementing the NAAQS. The Agencyalso plans to issue guidance to theStates on reducing the potential impacton small entities of implementing theNAAQS.

C. Impact on Reporting RequirementsThere are no reporting requirements

directly associated with the finalizationof ambient air quality standards undersection 109 of the Act (42 U.S.C. 7409).There are, however, reporting

requirements associated with relatedsections of the Act, particularly sections107, 110, 160, and 317 (42 U.S.C. 7407,7410, 7460, and 7617).

D. Unfunded Mandates Reform ActTitle II of the Unfunded Mandates

Reform Act of 1995 (UMRA), Pub. L.104–4, establishes requirements forFederal agencies to assess the effects oftheir regulatory actions on State, local,and tribal governments and the privatesector. Under section 202 of the UMRA,EPA generally must prepare a writtenstatement, including a cost-benefitanalysis, for proposed and final ruleswith ‘‘Federal mandates’’ that mayresult in expenditures by State, local,and tribal governments, in the aggregate,or by the private sector, of $100 millionor more in any one year. Thisrequirement does not apply if EPA isprohibited by law from consideringsection 202 estimates and analyses inadopting the rule in question. Beforepromulgating an EPA rule for which awritten statement is needed, section 205of the UMRA generally requires EPA toidentify and consider a reasonablenumber of regulatory alternatives andadopt the least costly, most cost-effective, or least burdensomealternative that achieves the objectivesof the rule. These requirements do notapply when they are inconsistent withapplicable law. Moreover, section 205allows EPA to adopt an alternative otherthan the least costly, most cost-effective,or least burdensome alternative if theAdministrator publishes with the finalrule an explanation of why thatalternative was not adopted. Before EPAestablishes any regulatory requirementsthat may significantly or uniquely affectsmall governments, including tribalgovernments, it must have developedunder section 203 of the UMRA a smallgovernment agency plan. The plan mustprovide for notifying potentiallyaffected small governments, enablingofficials of affected small governmentsto have meaningful and timely input inthe development of EPA regulatoryproposals with significant Federalintergovernmental mandates, andinforming, educating, and advisingsmall governments on compliance withthe regulatory requirements. Section 204of UMRA requires each agency todevelop ‘‘an effective process to permitelected officers of State, local and tribalgovernments *** to provide meaningfuland timely input’’ in the development ofregulatory proposals containing asignificant Federal intergovernmentalmandate.67

The EPA has determined that theprovisions of sections 202 and 205 ofthe UMRA do not apply to this decision.‘‘Unless otherwise prohibited by law,’’EPA is to prepare a written statementunder Section 202 of UMRA that is tocontain assessments and estimates ofthe costs and benefits of a rulecontaining a Federal mandate. Congressclarified that ‘‘unless otherwiseprohibited by law’’ referred to whetheran agency was prohibited fromconsidering the information in therulemaking process, not to whether anagency was prohibited from collectingthe information. The Conference Reporton UMRA states, ‘‘This section [202]does not require the preparation of anyestimate or analysis if the agency isprohibited by law from considering theestimate or analysis in adopting therule.’’ 141 Cong. Rec. H3063 (daily ed.March 13, 1995). Because the Clean AirAct prohibits EPA, when setting theNAAQS, from considering the types ofestimates and assessments described insection 202, UMRA does not requireEPA to prepare a written statementunder section 202.68 The requirementsin section 205 do not apply becausethose requirements only apply to rules‘‘for which a written statement isrequired under section 202 ***.’’

The EPA has determined that theprovisions of section 203 of UMRA donot apply to this decision. Section 203only requires the development of asmall government agency plan forrequirements with which smallgovernments might have to comply.Since setting the NAAQS does notestablish requirements with whichsmall governments might have tocomply, section 203 does not apply. The


69 One commenter argued that in reviewing theSO2 NAAQS, EPA determined that it need notrevise the SO2 NAAQS, but could instead pursuean alternative regulatory program under otherauthority. This commenter argued that EPA hassimilar flexibility in reviewing the PM and OzoneNAAQS, and thus UMRA requires EPA to identifythe least burdensome alternative (such as retainingthe current NAAQS) as part of that process. Asdiscussed more fully above at Unit IV of thispreamble, EPA does not agree that it has flexibilityto choose such an alternative; nor does EPA agreewith the commenter’s characterization of the actionit took in deciding not to revise the SO2 NAAQS.In fact, in deciding not to revise the SO2 NAAQS,EPA determined, for reasons independent of section303 of the Clean Air Act that a NAAQS revision wasnot warranted. See 61 FR 25566, 25575, May 22,1996.

EPA acknowledges, however, that anycorresponding revisions to associatedState implementation plan requirementsand air quality surveillancerequirements, 40 CFR part 51 and 40CFR part 58, respectively, might resultin such effects. Accordingly, EPA willaddress unfunded mandates asappropriate when it proposes anyrevisions to 40 CFR parts 51 and 58.

With regard to the outreach describedin UMRA section 204, EPA did followa process for providing elected officialswith an opportunity for meaningful andtimely input into the proposed NAAQSrevisions, although EPA did notdescribe this process in the proposal.The EPA conducted a series of pre-proposal outreach meetings with Stateand local officials and theirrepresentatives that permitted theseofficials to provide meaningful andtimely input on issues related to theNAAQS and the monitoring issuesassociated with them. Beginning inJanuary, 1996, EPA briefed State andlocal air pollution control officials atnational meetings with State andTerritorial Air Pollution ProgramAdministrators (STAPPA)/Associationof Local Air Pollution Control Officials(ALAPCO) in Washington DC, NorthCarolina, Chicago and Nevada. The EPAalso held briefings for the WashingtonDC representatives of several State andlocal organizations, including NationalConference of State Legislators, U.S.Conference of Mayors, NationalGovernors Association, and NationalLeague of Cities, and STAPPA/ALAPCO. EPA also held separatebriefings and discussions with State andlocal officials at meetings set up by theNational Governors Association, theU.S. Conference of Mayors and theCouncil of State Governments. The EPAalso conducted in-depth briefings ateach EPA regional office and regionalstaff also had several meetings anddiscussions with their Statecounterparts about the standards. Theefforts described above, which providedelected officials with opportunity formeaningful and timely input into theproposed NAAQS revisions, met anyrequirements imposed by section 204.The docket will contain a writtenstatement describing these outreachefforts, including a summary of thecomments and concerns presented byState, local, and tribal governments anda summary of EPA’s evaluation of thosecomments and concerns.

Several commenters disagreed withEPA that UMRA sections 202, 203 and205 do not apply to this decision. Thesecommenters argued that EPA is notprohibited from considering costs insetting NAAQS under the Clean Air Act

and applicable judicial decisions. Somecommenters also expressed the viewthat there is no conflict between UMRAand the Clean Air Act with regard to theNAAQS. These commenters argued thatUMRA and the NAAQS can be‘‘harmonized’’ by reading UMRA as aninformation gathering statute and thatEPA should therefore perform theanalyses required by UMRA, regardlessof whether costs may be considered.Finally, at least one commenter arguedthat in past NAAQS reviews, EPA didnot dispute its UMRA obligations.

As discussed more fully in Unit IV ofthis preamble, EPA is prohibited fromconsidering cost in setting the NAAQS.Given that fact (as noted in Unit IVpreamble), sections 202 and 205 do notapply.69 As the Conference Reportclarifies, UMRA itself states that thesection 202 estimates and analyses arenot required in cases such as theNAAQS, where an agency is prohibitedby law from considering section 202estimates and analyses. Reading UMRAin the manner suggested by thecommenters would effectively read thisprovision out of UMRA; UMRA containsan exception for rules like the NAAQS,it must be given effect.

With regard to EPA’s positionregarding UMRA in previous NAAQSreview exercises, EPA simply madeplain in those situations that because itdid not plan on revising the NAAQS, itdetermined, without further review, thatUMRA sections 202, 203 and 205 didnot apply. EPA thus stated that:

Because the Administrator has decided notto revise the existing primary NAAQS forSO2, this action will not impose any newexpenditures on governments or on theprivate sector, or establish any newregulatory requirements affecting smallgovernments. Accordingly, EPA hasdetermined that the provisions of section202, 203 and 205 do not apply to this finaldecision.

61 FR 25566, 25577, May 22, 1996; Seealso 61 FR 52852, 52856, October 8,1996 (Same statement for NO2 NAAQS).As this statement makes clear, EPA only

determined that UMRA sections 202,203 and 205 did not apply to theNAAQS when EPA fails to revise thestandard. Having made thatdetermination, EPA had no reason tocatalogue additional bases for findingUMRA inapplicable. Nothing in thatstatement was intended to precludeEPA, or precludes EPA, fromconcluding for other reasons (such asthose discussed above) that UMRA alsodoes not apply when EPA in fact revisesan applicable NAAQS.

E. Environmental JusticeExecutive Order 12848 requires that

each Federal agency make achievingenvironmental justice part of its missionby identifying and addressing, asappropriate, disproportionately highand adverse human health orenvironmental effects of its programs,policies, and activities on minoritiesand low-income populations. Theserequirements have been addressed tothe extent practicable in the RIA citedabove.

F. Submission to Congress and theComptroller General

Under 5 U.S.C. 801(a)(1)(A), as addedby the Small Business RegulatoryEnforcement Fairness Act of 1996(SBREFA), EPA submitted a reportcontaining this rule and other requiredinformation to the U.S. Senate, the U.S.House of Representatives, and theComptroller General of the UnitedStates prior to publication of the rule intoday’s Federal Register. This rule is a‘‘major rule’’ for purposes of SBREFA.

VIII. Response to Petition forAdministrator Browner’s Recusal

On March 13, 1997, the WashingtonLegal Foundation (WLF), filed a petitionwith EPA asking that I, Carol Browner,disqualify myself in rulemakingregarding the NAAQS for PM and O3.The petition claims that my publicstatements indicate a ‘‘clear andconvincing showing’’ that I had‘‘already decided to revise the NAAQSfor PM and ozone’’ and that I therefore‘‘could not give meaningfulconsideration’’ to comments adverse tothe proposed rule. On May 12, 1997,EPA’s General Counsel, Jonathan Z.Cannon, sent a letter to WLF regardingthe petition. This letter and the WLFpetition were then placed in the docketsfor the proposed O3 and PM standardspending ‘‘consideration and finalresponse in connection with theAgency’s final actions.’’

Contrary to WLF’s assertions, I havemaintained an open mind throughoutthese proceedings, and have basedtoday’s decisions on the rulemaking


record—including consideration ofcomments opposed to the proposal. Thelaw does not require the Administratorof EPA to disqualify herself merely forexpressing views on a proposedregulation; in fact, it is part of myresponsibility to engage in the publicdebate on the proposals. Moreover, theassertions in WLF’s petition do notaccurately represent my views. Thepetition takes quotes out of context andrepeatedly misinterprets my statements.For example, WLF quotes a statementthat I made at the Children’sEnvironmental Health NetworkResearch Conference as an indicationthat I had ‘‘prejudged the issue.’’However, my statement that ‘‘I will notbe swayed’’ did not refer to adopting theNAAQS as proposed. Instead, as is clearfrom reviewing the entire speech, I wasaddressing my broader concern aboutchildren’s health and the range of EPAstandards affecting children’s health. Ialso appeared at several congressionalhearings and testified before members ofCongress, some of whom were stronglyopposed to the proposals. At thosehearings, I explained the basis for theproposals and put forward the reasonswhy I concluded the proposals wereappropriate, given the informationbefore me at the time. At the same time,I made clear that I took very seriouslymy obligation to keep an open mind,and to consider fully and fairly allsignificant comments that the Agencyreceived. For these reasons and others,as set forth in Mr. Cannon’s May 12,1997 response to WLF, which I adopt infull, I have decided not to recuse myselffrom any aspect of considering revisionsto the NAAQS for O3 and PM.Accordingly, I am hereby denyingWLF’s petition.

IX. References

(1) American Thoracic Society. (1985)Guidelines as to what constitutes an adverserespiratory health effect, with specialreference to epidemiologic studies of airpollution. American Review of RespiratoryDisease.. 131: 666–668.

(2) Freas (1996) Ambient air qualityrelationships among alternative ozone airquality standards. Internal memorandumfrom Warren P. Freas to file, U.S. EPA,EMAD/OAQPS/OAR, RTP, NC, datedOctober 30, 1996. Docket No. A–95–58 ItemII–B–6.

(3) Freas (1997) Ambient air qualityrelationships for counties meeting alternativeair quality standards. Internal memorandumfrom Warren P. Freas to file, U.S. EPA,EMAD/OAQPS/OAR, RTP, NC, dated July 1,1997. Docket No. A–95–58 Item xxx.

(4) Heck, Walter W. And Ellis B. Cowling.January, 1997. EM Journal. ‘‘The Need for aLong Term Cumulative Secondary OzoneStandard - An Ecological Perspective.’’ Air

and Waste Management Association,Pittsburgh, PA.; pp. 23–33.

(5) Johnson, T; Capel, J.; Mozier, J.; McCoy,M. (1996a) Estimation of ozone exposuresexperienced by outdoor children in nineurban areas using a probabilistic version ofNEM. Prepared by IT/Air Quality Services forU.S. EPA, OAQPS; Research Triangle Park,NC, August.

(6) Johnson, T.; Capel, J.; McCoy, M.;Mozier, J. (1996b) Estimation of ozoneexposures experienced by outdoor workers innine urban areas using a probabilistic versionof NEM. Prepared by IT/Air Quality Servicesfor U.S. EPA, OAQPS; Research TrianglePark, NC, August.

(7) McClellan, R. O., (1989) Letter fromChairman of Clean Air Scientific AdvisoryCommittee to the EPA Administrator, datedMay 1, 1989. EPA–SAB-CASAC-LTR–89–019.

(8) Richmond (1997) Supplemental ozoneexposure and health risk analyses. Internalmemorandum from Harvey M. Richmond toKaren M. Martin, U.S. EPA, AQSSD/OAQPS/OAR, RTP, NC, dated February 11, 1997.Docket No. A–95–58 Item IV–A–1.

(9) Seitz (1996) Revocation date for theexisting 1–hour ozone standards. Internalmemorandum from John S. Seitz to Mary D.Nichols, U.S. EPA, OAQPS/OAR, RTP, NC,dated November 20, 1996. Docket No. A–95–59 Item II–B–3.

(10) Thurston, G.D.; Ito, K.; Kinney, P.L.;Lippmann, M. (1992) A multi-year study ofair pollution and respiratory hospitaladmissions in three New York Statemetropolitan areas: results for 1988 and 1989summers. Journal of Exposure Analysis andEnvironmental Epidemiology. 2:429–450.

(11) U.S. Department of Health and HumanServices (1996) Vital and health statistics:current estimates from the national healthinterview survey, 1994. Hyattsville, MD:Public Health Service, National Center forHealth Statistics; DHHS publication no.(PHS) 96–278.

(12) U.S. Environmental Protection Agency(1996a) Air quality criteria for Ozone andrelated photochemical oxidants. ResearchTriangle Park, NC: Office of Health andEnvironmental Assessment, EnvironmentalCriteria and Assessment Office; EPA reportnos. EPA/600/AP–93/004a–c.

(13) U.S. Environmental Protection Agency(1996b) Review of the national ambient airquality standards for ozone: assessment ofscientific and technical information. OAQPSstaff paper. Research Triangle Park, NC:Office of Air Quality Planning and Standards;EPA report no. EPA–452/R–96–007.Available from: NTIS, Springfield, VA;PB96–203435.

(14) Whitfield, R.G.; Biller, W.F.; Jusko,M.J.; Keisler, J.M. (1996) A probabilisticassessment of health risks associated withshort-term exposure to tropospheric ozone.Report prepared for U.S. EPA, OAQPS.Argonne National Laboratory; Argonne, IL,June. (For copies, contact Harvey M.Richmond, U.S. Environmental ProtectionAgency, OAQPS, MD–15, Research TrianglePark, N.C. 27711, (919) 541–5271.)

(15) Wolff, G. T., (1995a) Letter fromChairman of Clean Air Scientific AdvisoryCommittee to the EPA Administrator, dated

November 28, 1995. EPA–SAB–CASAC–LTR–96–001.

(16) Wolff, G. T., (1995b) Letter fromChairman of Clean Air Scientific AdvisoryCommittee to the EPA Administrator, datedNovember 30, 1995. EPA–SAB–CASAC–LTR–96–002.

(17) Wolff, G. T., (1996) Letter fromChairman of Clean Air Scientific AdvisoryCommittee to the EPA Administrator, datedApril 4, 1996. EPA–SAB–CASAC–LTR–96–006.

List of Subjects in 40 CFR Part 50Environmental protection, Air

pollution control, Carbon monoxide,Lead, Nitrogen dioxide, Ozone,Particulate matter, Sulfur oxides.

Dated: July 16, 1997.

Carol M. Browner,Administrator.

Therefore, for the reasons set forth inthe preamble, title 40, chapter I, part 50of the Code of Federal Regulations isamended as follows:

PART 50—NATIONAL PRIMARY ANDSECONDARY AMBIENT AIR QUALITYSTANDARDS

1. The authority citation for part 50continues to read as follows:

Authority: Secs. 109 and 301(a), Clean AirAct, as amended (42 U.S.C. 7409, 7601(a)).

2. Section 50.9 is revised to read asfollows:

§ 50.9 National 1–hour primary andsecondary ambient air quality standards forozone.

(a) The level of the national 1-hourprimary and secondary ambient airquality standards for ozone measured bya reference method based on AppendixD to this part and designated inaccordance with part 53 of this chapter,is 0.12 parts per million (235 µg/m3).The standard is attained when theexpected number of days per calendaryear with maximum hourly averageconcentrations above 0.12 parts permillion (235 µg/m3) is equal to or lessthan 1, as determined by Appendix H tothis part.

(b) The 1–hour standards set forth inthis section will no longer apply to anarea once EPA determines that the areahas air quality meeting the 1–hourstandard. Area designations are codifiedin 40 CFR part 81.

3. Section 50.10 is added to read asfollows:

§ 50.10 National 8–hour primary andsecondary ambient air quality standards forozone.

(a) The level of the national 8–hourprimary and secondary ambient airquality standards for ozone, measured


by a reference method based onAppendix D to this part and designatedin accordance with part 53 of thischapter, is 0.08 parts per million (ppm),daily maximum 8–hour average.

(b) The 8–hour primary andsecondary ozone ambient air qualitystandards are met at an ambient airquality monitoring site when theaverage of the annual fourth-highestdaily maximum 8–hour average ozoneconcentration is less than or equal to0.08 ppm, as determined in accordancewith Appendix I to this part.

4. Appendix D is amended by revisingreferences 8 and 9 and by removing allof the text and figures immediatelyfollowing ‘‘Figure 2, Schematic Diagramof a Typical UV Photometric CalibrationSystem (Option 1), through the end ofAppendix D.

Appendix D to Part 50—MeasurementPrinciple and Calibration Procedure forthe Measurement of Ozone in theAtmosphere

* * * * *6. References.

* * * * *8. Transfer Standards for Calibration of

Ambient Air Monitoring Analyzers forOzone, EPA publication number EPA–600/4–79–056, EPA, National Exposure ResearchLaboratory, Department E, (MD–77B),Research Triangle Park, NC 27711.

9. Technical Assistance Document for theCalibration of Ambient Ozone Monitors, EPApublication number EPA–600/4–79–057,EPA, National Exposure Research Laboratory,Department E, (MD–77B), Research TrianglePark, NC 27711.

* * * * *

Appendix E [Removed and Reserved]

5. Appendix E is removed andreserved.

6. Appendix H is amended by revisingthe appendix heading to read‘‘Appendix H To Part 50—Interpretationof The 1-Hour Primary and SecondaryNational Ambient Air Quality Standardsfor Ozone’’.

7. Appendix I is added to read asfollows:

Appendix I to Part 50—Interpretation ofthe 8–Hour Primary and SecondaryNational Ambient Air QualityStandards for Ozone

1. General.This appendix explains the data handling

conventions and computations necessary fordetermining whether the national 8–hourprimary and secondary ambient air qualitystandards for ozone specified in § 50.10 aremet at an ambient ozone air qualitymonitoring site. Ozone is measured in theambient air by a reference method based onAppendix D of this part. Data reporting, data

handling, and computation procedures to beused in making comparisons betweenreported ozone concentrations and the levelof the ozone standard are specified in thefollowing sections. Whether to exclude,retain, or make adjustments to the dataaffected by stratospheric ozone intrusion orother natural events is subject to the approvalof the appropriate Regional Administrator.

2. Primary and Secondary Ambient AirQuality Standards for Ozone.

2.1 Data Reporting and HandlingConventions.

2.1.1 Computing 8–hour averages. Hourlyaverage concentrations shall be reported inparts per million (ppm) to the third decimalplace, with additional digits to the rightbeing truncated. Running 8–hour averagesshall be computed from the hourly ozoneconcentration data for each hour of the yearand the result shall be stored in the first, orstart, hour of the 8–hour period. An 8–houraverage shall be considered valid if at least75% of the hourly averages for the 8–hourperiod are available. In the event that only 6(or 7) hourly averages are available, the 8–hour average shall be computed on the basisof the hours available using 6 (or 7) as thedivisor. (8–hour periods with three or moremissing hours shall not be ignored if, aftersubstituting one-half the minimum detectablelimit for the missing hourly concentrations,the 8–hour average concentration is greaterthan the level of the standard.) The computed8–hour average ozone concentrations shall bereported to three decimal places (theinsignificant digits to the right of the thirddecimal place are truncated, consistent withthe data handling procedures for the reporteddata.)

2.1.2 Daily maximum 8–hour averageconcentrations. (a) There are 24 possiblerunning 8–hour average ozone concentrationsfor each calendar day during the ozonemonitoring season. (Ozone monitoringseasons vary by geographic location asdesignated in part 58, Appendix D to thischapter.) The daily maximum 8–hourconcentration for a given calendar day is thehighest of the 24 possible 8–hour averageconcentrations computed for that day. Thisprocess is repeated, yielding a dailymaximum 8–hour average ozoneconcentration for each calendar day withambient ozone monitoring data. Because the8–hour averages are recorded in the starthour, the daily maximum 8–hourconcentrations from two consecutive daysmay have some hourly concentrations incommon. Generally, overlapping dailymaximum 8–hour averages are not likely,except in those non–urban monitoringlocations with less pronounced diurnalvariation in hourly concentrations.

(b) An ozone monitoring day shall becounted as a valid day if valid 8–houraverages are available for at least 75% ofpossible hours in the day (i.e., at least 18 ofthe 24 averages). In the event that less than75% of the 8–hour averages are available, aday shall also be counted as a valid day ifthe daily maximum 8–hour averageconcentration for that day is greater than thelevel of the ambient standard.

2.2 Primary and Secondary Standard-related Summary Statistic. The standard-

related summary statistic is the annualfourth-highest daily maximum 8–hour ozoneconcentration, expressed in parts per million,averaged over three years. The 3–year averageshall be computed using the three mostrecent, consecutive calendar years ofmonitoring data meeting the datacompleteness requirements described in thisappendix. The computed 3–year average ofthe annual fourth-highest daily maximum 8–hour average ozone concentrations shall beexpressed to three decimal places (theremaining digits to the right are truncated.)

2.3 Comparisons with the Primary andSecondary Ozone Standards. (a) The primaryand secondary ozone ambient air qualitystandards are met at an ambient air qualitymonitoring site when the 3–year average ofthe annual fourth-highest daily maximum 8–hour average ozone concentration is less thanor equal to 0.08 ppm. The number ofsignificant figures in the level of the standarddictates the rounding convention forcomparing the computed 3–year averageannual fourth-highest daily maximum 8–hour average ozone concentration with thelevel of the standard. The third decimal placeof the computed value is rounded, withvalues equal to or greater than 5 rounding up.Thus, a computed 3–year average ozoneconcentration of 0.085 ppm is the smallestvalue that is greater than 0.08 ppm.

(b) This comparison shall be based on threeconsecutive, complete calendar years of airquality monitoring data. This requirement ismet for the three year period at a monitoringsite if daily maximum 8–hour averageconcentrations are available for at least 90%,on average, of the days during the designatedozone monitoring season, with a minimumdata completeness in any one year of at least75% of the designated sampling days. Whencomputing whether the minimum datacompleteness requirements have been met,meteorological or ambient data may besufficient to demonstrate that meteorologicalconditions on missing days were notconducive to concentrations above the levelof the standard. Missing days assumed lessthan the level of the standard are counted forthe purpose of meeting the data completenessrequirement, subject to the approval of theappropriate Regional Administrator.

(c) Years with concentrations greater thanthe level of the standard shall not be ignoredon the ground that they have less thancomplete data. Thus, in computing the 3–year average fourth maximum concentration,calendar years with less than 75% datacompleteness shall be included in thecomputation if the average annual fourthmaximum 8–hour concentration is greaterthan the level of the standard.

(d) Comparisons with the primary andsecondary ozone standards are demonstratedby examples 1 and 2 in paragraphs (d)(1) and(d) (2) respectively as follows:

(1) As shown in example 1, the primaryand secondary standards are met at thismonitoring site because the 3–year average ofthe annual fourth-highest daily maximum 8–hour average ozone concentrations (i.e., 0.084ppm) is less than or equal to 0.08 ppm. Thedata completeness requirement is also metbecause the average percent of days withvalid ambient monitoring data is greater than


90%, and no single year has less than 75%data completeness.

EXAMPLE 1. AMBIENT MONITORING SITE ATTAINING THE PRIMARY AND SECONDARY OZONE STANDARDS

Year PercentValid Days

1st HighestDaily Max

8–hourConc. (ppm)

2nd HighestDaily Max

8–hourConc. (ppm)

3rd HighestDaily Max

8–hourConc. (ppm)

4th HighestDaily Max

8–hourConc. (ppm)


8–hourConc. (ppm)

1993 .................................................................................. 100% 0.092 0.091 0.090 0.088 0.085

1994 .................................................................................. 96% 0.090 0.089 0.086 0.084 0.080

1995 .................................................................................. 98% 0.087 0.085 0.083 0.080 0.075

Average ...................................................................... 98% 0.084

(2) As shown in example 2, the primaryand secondary standards are not met at thismonitoring site because the 3–year average ofthe fourth-highest daily maximum 8–hour

average ozone concentrations (i.e., 0.093ppm) is greater than 0.08 ppm. Note that theozone concentration data for 1994 is used inthese computations, even though the data

capture is less than 75%, because the averagefourth-highest daily maximum 8–houraverage concentration is greater than 0.08ppm.

EXAMPLE 2. AMBIENT MONITORING SITE FAILING TO MEET THE PRIMARY AND SECONDARY OZONE STANDARDS

Year PercentValid Days

1st HighestDaily Max

8–hourConc. (ppm)

2nd HighestDaily Max

8–hourConc. (ppm)

3rd HighestDaily Max

8–hourConc. (ppm)


8–hourConc. (ppm)


8–hourConc. (ppm)

1993 .................................................................................. 96% 0.105 0.103 0.103 0.102 0.102

1994 .................................................................................. 74% 0.090 0.085 0.082 0.080 0.078

1995 .................................................................................. 98% 0.103 0.101 0.101 0.097 0.095

Average ...................................................................... 89% 0.093

3. Design Values for Primary andSecondary Ambient Air Quality Standardsfor Ozone.

The air quality design value at amonitoring site is defined as thatconcentration that when reduced to the level

of the standard ensures that the site meets thestandard. For a concentration-based standard,the air quality design value is simply thestandard-related test statistic. Thus, for theprimary and secondary ozone standards, the3–year average annual fourth-highest daily

maximum 8–hour average ozoneconcentration is also the air quality designvalue for the site.[FR Doc. 97–18580 Filed 7–17–97; 8:45 am]

BILLING CODE 6560–50–F

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