REDUCTION OF HIGHLY REACTIVE VOLATILE ORGANIC COMPOUNDS &VARIABLE EMISSIONS IN HOUSTON/GALVESTON:MONITORING, MODELING, MEASURING, RULEMAKING

David AllenDepartment of Chemical Engineering, andCenter for Energy and Environmental ResourcesUniversity of Texas(512-471-0049; allen@che.utexas.edu)

The Houston-Galveston area is a severe ozone non-attainment area; costs and benefits of controls have been estimated to be ~$5 billion/yrThe current EPA approved State Implementation Plan (SIP, approved in 2000) calls for significant NOx emission reductions (approximately 70% of the 2007 inventory; 90+% for point sources); SIP also called for some VOC emission reductions Proposed new plan adds emission reductions for highly reactive VOCs from industrial facilities and applies 80%, rather than 90% industrial NOx emission reductions

Outline Why focus on Highly Reactive Volatile Organic Compounds (HRVOCs)? Why are we considering variability in emissions? This presentation will provide an overview of the scientific basis for decision-making Impact of scientific findings on air quality policy and current direction of technical analyses impacting policy decisions

Focus on HRVOCs emerged out of the Texas Air Quality Study -2000(TEXAQS - 2000)

(www.utexas.edu/research/ceer/texaqs/) (www.utexas.edu/research/ceer/texaqsarchive)

TEXAQS - 2000: Study overviewStudy conducted from approximately August 15 - September 15 Approximately 300 investigators 5 aircraft5 major ground chemistry sitesCoordinated with Houston fine particulate matter Supersite sampling intensive

TexAQS and other research programs address key areas of uncertaintyEmission inventoriesChemical and physical processes in the atmosphere, particularly those leading to rapid and efficient ozone formation (a.k.a. ozone spikes)Regional air quality modeling/air quality policies

Chemical and physical processes in the atmosphere: Rapid ozone formation events

TexAQS data have played a crucial role in understanding these events: Physical insights

Hydrocarbon ReactivitiesTop 10% of samples exhibit reactivities that are 4x the mean value. For the most part the highest reactivities are geographically associated with industries in the Ship Channel.

Apportionment of reactivity for high reactivity samplesFor the high reactivity samples, low molecular weight alkenes (propene, ethene and butenes) are a major source of hydrocarbon reactivity for ozone formation.Twin Otter VOC SamplesAverage for 26 samples with k>10 s-1

TexAQS showed us that HRVOCs are important, but what is relative importance of short, episodic releases vs. continuous, steady emissions?

HRVOC emissionsHRVOCs defined as ethylene, propylene, butylenes and 1,3-butadieneContinuous emissions to be addressed with a CAP (and trade?) programEmission events to be handled through a short term cap

Conceptual issueIn most of US, industrial emissions are relatively constant or are small enough that meteorology is cause of worst conditions In Houston, both meteorology and emissions are cause of worst conditions

Conceptual issue

Estimating variability for continuous emissions

Event Emissions and their impact on ozone formation in the Houston Galveston Area

Key QuestionsAre the magnitudes of emission events, singularly and collectively, significant relative to routine emissions? What are the characteristics of the events in terms of time, space, and composition? How do the events influence ozone formation?

TCEQ event database, established in early 2003

First 11 Months of reporting:

NOx emission event emissions are small compared to annual average emissions

At specific times and locations, VOC and HRVOC emissions can be large relative to annual average emissionsAverage hourly emissions of all point sources

Total mass of over 4 millions pounds (2000 tons) contributes 4% to the 45,000 tons of VOC emitted over a single year from point sources in the four counties. 14 times (18 hours) during the eleven-month period, event emissions exceed the annual average for all facilities in the region. VOCs4,000,000 lb

Harvey Jeffries - The figure fonts could at least be made BOLDAnd some of the most important "notes" couldbe colored RED, like total emissions values

The inserted

Total mass of over 1.6 millions pounds (830 tons) is ~12% of the 6800 tons of HRVOC emitted over a single year from point sources in the four counties. 29 times (115 hours) during the eleven-month period, event emissions exceed the annual average. HRVOCs1,650,000 lb

1,3-Butadiene~50,000 lbButenes~100,000 lbPropene~500,000 lbEthene ~1,000,000 lb

Harvey Jeffries - The messages on these figures will not be lost if these two and the next two are combined on one slide

What are the characteristics of the events in terms of time, space, and composition?

Most HRVOC events last less than a day, many last less than an hour Largest number of events is from events of 100-1000 lb, but most of the mass is associated with events greater than 1000 lb, which occur, on average, several times per week 2-3 times per weekDailyLess than 24 hours

Conceptual modelEvents with emissions of more than 1000 pounds of HRVOCs occur several times per week, on average; events with emissions of more than 10,000 pounds of HRVOCs occur several times per month, on averageMany are relatively short (well under one hour in duration)Among the HRVOCs, ethene and propene dominateEvents occur primarily in Harris and Brazoria counties at chemical manufacturing facilities

Harvey Jeffries - changed "orruring" to "occur"

What are the consequences for ozone formation?

Example of worst case scenario: Monitoring data from a 6700 lb, 30 minute ethylene release at LaPorte

10,000+ lb ethylene release at LaPorte, (6700 lb between 11 and 11:25 AM) 3/27/2002

Short term ozone enhancements of up to 100 ppb

Add Event to Air Quality Model(most recent version with 1-km resolution)Without EventWith EventLayer One149.9 ppb vs 203.0 ppb

Outline Why Highly Reactive Volatile Organic Compounds (HRVOCs)? Why are we considering variability in emissions? An overview of the scientific basis for decision-making Impact of scientific findings on air quality policy and current direction of technical analyses impacting policy decisions

Actions taken by the TCEQ and current technical analysesBased on the data from TexAQS, which indicate that VOC emissions from industrial facilities are responsible for rapid and efficient ozone formation, new rules have been proposed for emissions of highly reactive volatile organic compounds (HRVOCs) from flares, cooling towers and fugitive sources Balance between NOx and HRVOC emission controls reevaluated, balance between short term and annual HRVOC emissions being evaluated; focus of work at UT is on short term releases and on characterizing scientific uncertainties

Summary Overview of major findings from TexAQS Shift in focus to reactive hydrocarbonsImpact of findings on air quality policy Shift in focus to reactive hydrocarbons with a focus on most reactive hydrocarbons caps on HRVOC emissionsCurrent direction of technical analyses impacting policy decisions (Highly Reactive Volatile Organic Compounds, HRVOCs) Relative importance of annual and short term limits on HRVOC emissions