IMPROVEMENTS TO THE CAL3QHCR MODELdocs.trb.org/prp/14-5142.pdf · IMPROVEMENTS TO THE CAL3QHCR...
Transcript of IMPROVEMENTS TO THE CAL3QHCR MODELdocs.trb.org/prp/14-5142.pdf · IMPROVEMENTS TO THE CAL3QHCR...
Michael Claggett 1
IMPROVEMENTS TO THE CAL3QHCR MODEL
Michael Claggett, Ph.D. (corresponding author)
Air Quality Modeling Specialist
U.S. Department of Transportation
Federal Highway Administration Resource Center
4001 Office Court Drive, Suite 801
Santa Fe, New Mexico 87507
(505) 820-2047
Submission Date: November 15, 2013
Word Count:
Text = 4,042
Tables (1 @ 250 words) = 250
Figures (6 @ 250 words) = 1,500
Total = 5,792
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ABSTRACT
The CAL3QHCR model is designated as a preferred model for regulatory applications involving
highways in the U.S. Environmental Protection Agency’s (EPA) Guideline on Air Quality
Models. As a result, it is used for a number of regulatory and non-regulatory applications,
including project-level conformity analyses, highway air quality analyses relevant to the National
Environmental Policy Act; health impact studies; and research. Model improvements have been
made to: 1) simplify and update the input file structure; 2) allocate receptor and link arrays at
runtime; 3) eliminate the internal rounding of 1-hour average concentration predictions; 4)
enhance the emission, traffic, and signalization (ETS) pattern function to account for month of
year and hour of day variations in addition to day of week variations; 5) supplement the ability to
consider background concentrations as a function of ETS patterns; 6) add the capability to
process multiple years of meteorology in a concatenated file; and 7) update the output file
structure. These improvement were made without affecting the concentration estimates
produced by CAL3QHCR and as such, the preferred status of the model is unchanged as
provided for in Title 40 of the Code of Federal Regulations, Part 51, Appendix W, Section
3.1.2b. Two non-regulatory options have also been added: 1) using meteorology processed by
the AERMOD meteorological processor, AERMET and 2) estimating downwind dispersion
based on the AERMOD formulation for computing vertical and horizontal dispersion
coefficients.
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INTRODUCTION
Provided is a description of updates made to the CAL3QHCR model to improve its use for
regulatory quantitative hot-spot analyses of transportation projects and similar purposes as with
air quality analyses relevant to the National Environmental Policy Act process. Such analyses
involve predictions of likely future localized concentrations of carbon monoxide (CO),
particulate matter (PM) of size ≤ 2.5 µm, PM of size ≤ 10 µm, nitrogen dioxide (NO2) and/or
other pollutants in the ambient air and comparisons of those concentrations to relevant National
Ambient Air Quality Standards or other air quality criteria.
CAL3QHCR is part of the CAL3 series of models. These models share the line source
dispersion algorithm of the CALINE3 model developed by Paul Benson (1). A vehicle queuing
algorithm was incorporated into the CAL3QHC model by Guido Schattanek and June Kahng (2)
for predicting pollutant concentrations near signalized intersections. Capabilities to account for
the hour-by-hour variability in vehicle emissions and meteorology were added to the
CAL3QHCR model by Peter Eckhoff and Thomas Braverman (3).
The U.S. Environmental Protection Agency’s (EPA) CAL3QHCR model (3) is
designated as a preferred model for regulatory applications involving highways in their
Guideline on Air Quality Models (4). The American Meteorological Society/EPA Regulatory
Model (5) (AERMOD) is recommended (4) for a wide range of regulatory applications in all
types of terrain and can be used to simulate lines sources “if point and volume sources are
appropriately combined” (4).
CAL3QHCR was specifically developed for highway applications based on research
conducted near highways. AERMOD was developed for industrial source applications and its
use has been extended to highways through the point, volume, and area source algorithms
incorporated in the model. The latest line source configuration added to AERMOD relies on the
existing area source algorithm. The turbulent wake generated by vehicles operating on highways
and its influence on near-field dispersion is not inherently accounted for by AERMOD. The U.S.
EPA continues to develop highway models, including AERLINE and RLINE.
CAL3QHCR remains the model of choice by many State Departments of Transportation
because of: 1) their familiarity with the CAL3 series of models – CALINE3 (1) and CAL3QHC
(2); 2) consistency with other dispersion modeling conducted in the highway air quality analysis
– there is no AERMOD alternative to CALINE3 or CAL3QHC; 3) the computational efficiency
of CAL3QHCR over AERMOD – CAL3QHCR runs approximately 6 times faster; and 4)
CAL3QHCR typically provides lower results – a factor of 2 for some applications (6).
MODEL IMPROVEMENTS
The CAL3QHCR model has been updated to improve its use for the special regulatory
applications involving highways as specified in Title 40 of the Code of Federal Regulations, Part
51, Appendix W (4) and for similar purposes. Section 3.1b 40 CFR 51, Appendix W addresses
the issue where changes are made to a preferred model such as CAL3QHCR without affecting
the concentration estimates. The modifications made as described enable the use of the model
and only affect the format and averaging time of the model results, not the concentration
estimates. Three code enhancements have been made to improve the computational precision of
the CAL3QHCR predictions. The model improvements that have been made include:
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Simplify and update the input file structure
Allocate receptor and link arrays at runtime
Eliminate the internal rounding of 1-hour average concentration predictions
Enhance the emission, traffic, and signalization (ETS) pattern function to account for
month of year and hour of day variations in addition to day of week variations
Supplement the ability to consider background concentrations as a function of ETS
patterns
Add the capability to process multiple years of meteorology in a concatenated file
Update the output file structure
An input file consists of data records organized in six groupings: 1) file management; 2)
program controls and site variables; 3) receptor locations; 4) ETS patterns; 5) background
concentrations; and 6) link configurations. The structure of the input file was revised to integrate
file management, thus eliminating the need for a separate control file as in previous versions of
the model. Data records are consolidated to minimize the number required. Comment lines and
blank lines can be used to annotate an input file. A five character pathway label for data records
is incorporated. Its function is to provide a means to distinguish data records.
The preset limits on the numbers of receptors and links that can be considered in a
simulation is removed by allocating variable arrays at runtime. The computational precision of
concentration predictions is enhanced by eliminating internal rounding to the nearest tenth of a
microgram per cubic meter (g/m3) or parts per million (ppm) for CO or parts per billion (ppb)
for NO2. Also, the number of significant figures used for molecular weight and molar volume
values were increased for converting concentration units from µg/m3 to ppm and ppb.
Intermediate computation files are no longer employed. Previously, in the exchange of
information among the files, emission factors used in the concentration predictions were
truncated to the nearest hundredth of a gram per vehicle-mile (g/veh-mi). The three
computational refinements described are especially important in increasing the precision of low
concentration predictions. The revised CAL3QHCR model produces concentration estimates
equivalent to the estimates obtained using the U.S. EPA’s 12355 version of the model. Updates
are in progress based on the U.S. EPA’s most current version of the model dated 13196.
Perhaps the most significant change that was made to improve the applicability and ease
of use of the CAL3QHCR model is the advanced function to account for the variability of
emissions, traffic, and signalization patterns by month of year, hour of day, and day of week.
ETS patterns are used to reflect the detail of information available. Near the bottom end of the
range, vehicle activity may be characterized by season during the year, by peak and off-peak
periods during the day, and by weekday versus weekend. At the top end of the range, vehicle
activity may be characterized by month, hour, and day patterns. The data elements included in
an input file can correspond to the level of detail of the information available. The variability of
background concentrations may also be expressed according to ETS patterns.
A key feature that has been added to facilitate design value calculations is the capability
to process multiple years of meteorology in a single simulation. Calculations of the project
contribution to the design value are now made within the CAL3QHCR model. A number of
modifications to the output structure have also been made for design value reporting and to
support off-model design value calculations. Concentrations attributable to the project are
added to the background concentration to determine design values expressed statistically for
direct comparison to each applicable National Ambient Air Quality Standard. For instance, high
2nd high 1-hour and 8-hour average CO concentrations; average high quarterly 24-hour and
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average annual PM2.5 concentrations over a 5-year meteorological record (7); high 6th high 24-
hour PM10 concentrations over a 5-year meteorological record; and average high 8th high (98th
percentile) 1-hour NO2 concentrations over a 5-year meteorological record (8).
A pollutant name of up to five characters may be specified by means of the MODE
parameter. MODE has no effect on the concentration predictions made; it only affects the
pollutant label, format, and averaging time of the results. Designations that currently control the
pollutant label, format, and averaging time are 'CO', 'PM2.5', 'PM-10', 'NO2', and 'OTHER'.
Additional designations are used as the pollutant label; the format and averaging time are as
provided for MODE = 'OTHER'.
DATA REQUIREMENTS
The data needed to complete a CAL3QHCR model run consists of:
1. Receptor locations
a. receptor name
b. location coordinates (user specified units)
c. height of breathing zone (user specified units)
2. Highway configurations
a. traffic flow (free-flow or queue)
b. link name
c. centerline coordinates (user specified units)
d. source height (user specified units)
e. mixing zone width (user specified units)
3. Emissions
a. traffic volume (vph)
b. emission factor (g/v-mi for free-flow or g/v-hr for queue)
c. average total signal cycle length (s) for queue links
d. average red signal cycle length (s) for queue links
e. clearance lost time (s) for queue links
f. saturation flow rate (vphpl) for queue links
g. signal type (pre-timed, actuated, or semi-actuated) for queue links
h. arrival rate (worst, below average, average, above average, or best) for queue
links
4. Meteorology
a. averaging time (min)
b. surface roughness (cm)
c. settling velocity (cm/s)
d. deposition velocity (cm/s)
e. background concentration (ppm for CO; ppb for NO2; otherwise, ug/m3)
f. external, preprocessed data file
i. wind flow vector (degrees from north)
ii. wind speed (m/s)
iii. ambient temperature (K)
iv. stability class (1 through 6)
v. rural mixing height (m)
vi. urban mixing height (m)
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INPUT FILE STRUCTURE
Data records are entered in free format (meaning at least one space or comma is required to
delimit the fields) in six groupings:
1. File management
2. Program controls and site variables
3. Receptor locations
4. ETS patterns
5. Background concentrations
6. Link configurations
Comment lines and blank lines can be used to annotate an input file. The information
provided is ignored by the program if the first two characters on a line contain two asterisks or
two spaces. A five character pathway label for data records is incorporated. Its function is to
provide a means to distinguish data records. Avoid using two asterisks or two blanks as the first
two characters of a pathway label or the data record provided will be ignored. All fields in a
data record must contain a valid entry or the model will fail to complete its execution.
Figure 1 illustrates the new input file structure, presenting the sequence of each data
record and the data fields within a record. This information is also provided in an Excel®
workbook that may be used as a template for constructing an input file. Some data records, such
as receptors and link configurations, will require rows to be inserted in the workbook in the
correct sequence to accommodate extra data. Once completed, save as a CSV (comma
delimited) file. Such a file will require additional editing to remove extraneous commas. A
quick method for accomplishing this is to substitute a space ' ' for a comma ',' using a text editor.
MODEL OUTPUT
The basic descriptive output of the original CAL3QHCR model has been retained. Model
printout consists of sections and subsections containing general information such as site and
meteorological constants, link data constants, and receptor data, plus model results for averaging
times pertinent to the pollutant analyzed. A number of refinements to the model printout have
been made including: 1) increase the number of significant figures of the concentration predict-
ions reported; 2) provide the calendar year to identify the time period of the meteorological
record associated with the predicted concentrations; and 3) stipulate the 6th highest (or 8th highest
for NO2) concentrations in the primary and secondary averages table. The project contribution
component to design values has also been added to the model printout. Figures 2 through 5
illustrate the design value reporting contained in the model printout (edited for illustration
purposes).
The link output file of the original CAL3QHCR model has been replaced by an ETS
output file of variables as a function of month of year, day of week, and hour of day patterns.
Capabilities to produce post files and plot files of model results have also been added. Post files
contain concurrent model results of 1-hour and 8-hour CO concentrations; 24-hour and annual
average PM2.5, PM10, other pollutant concentrations; or 1-hour and annual average NO2
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FIGURE 1 Input File Structure.
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FIGURE 1 Input File Structure (continued).
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FIGURE 2 1-hour and 8-hour CO Design Values.
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FIGURE 3 Quarterly 24-hour and Average Annual PM2.5 Design Values.
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FIGURE 4 24-hour PM10 Design Values.
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FIGURE 5 1-hour and Average Annual NO2 Design Values.
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concentrations at each receptor for each year of meteorological data provided. Plot files contain
high value model results of 2nd high 1-hour and 8-hour CO concentrations; average quarterly 24-
hour and average annual PM2.5 concentrations; 6th high 24-hour and average annual PM10
concentrations; average 8th high 1-hour and average annual NO2 concentrations; or 24-hour and
average annual for other pollutant concentrations over the length of the meteorological data
record provided.
REGULATORY STATUS OF THE IMPROVED CAL3QHCR MODEL
Improvements to the CAL3QHCR model were made without affecting the concentration
estimates produced by the model. Table 1 provides a comparison of concentration estimates
produced by the improved CAL3QHCR model versus the U.S. EPA version dated 12355.
Updates are in progress based on the U.S. EPA’s most current regulatory version of the model
dated 13196. Matching results are obtained from the two models for the detailed test case
represented. There is an inconsequential (less than 0.01%) difference between predictions of the
maximum 5-year average concentrations. The reason for the difference has not been confirmed,
but is most likely due to differences in the precision of the computations between two computer
programs. Title 40 of the Code of Federal Regulations, Part 51, Appendix W (4), Section 3.1.2b
addresses the issue where “changes are made without affecting the concentration estimates”.
The U.S. EPA has also distributed a memo (9) regarding clarification on the regulatory status of
air dispersion models, in particular proprietary versions of AERMOD. The determination of
acceptability of a model is a U.S. EPA Regional Office responsibility. Typically, as stipulated in
Appendix W, “when any changes are made, the Regional Administrator should require a test
example to demonstrate that the concentration estimates are not affected” (4).
METEOROLOGICAL DATA PROCESSING
Hourly meteorology is required to characterize the atmospheric diffusion and transport of motor
vehicle emissions in a CAL3QHCR simulation. CAL3Rmet is a utility program developed for
creating meteorological data sets for use in the CAL3QHCR model based on the U.S. EPA’s
Meteorological Processor for Regulatory Models (MPRM) (10). CAL3Rmet provides access to
more readily available meteorological data sets as processed by the EPA’s AERMOD
Meteorological Preprocessor (AERMET) program (11). The CAL3met process is completed in
up to 6 steps:
STEP 1 - Assemble Surface and Upper Air data from AERMET processed files
STEP 2 - Extract and QA data by completing MPRM Stage 1 processing
STEP 3 - Merge data by completing MPRM Stage 2 processing
STEP 4 - Create a file for use in the CAL3QHCR model by completing MPRM Stage
3 processing
STEP 5 - Add urban mixing heights based on the U.S. EPA's AERMOD formulation
(optional)
STEP 6 – Substitute values for missing meteorological data (optional).
CAL3Rmet helps ensure consistency among data sets developed using the U.S. EPA’s AERMET
and MPRM processors.
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TABLE 1 Comparison of Concentration Estimates.
Improved CAL3QHCR U.S. EPA CAL3QHCR 12355
Year: 2006 2007 2008 2009 2010 2006 2007 2008 2009 2010 Max 1-hr Avg 9.33193 10.3298 9.16412 9.77849 10.0959 9.3319 10.3298 9.1641 9.7785 10.0959 Receptor 117 117 117 117 117 117 117 117 117 117 Wind Direction 300 314 298 305 320 300 314 298 305 320 Julian Day 65 14 84 30 34 65 14 84 30 34 Hour 7 8 8 8 7 7 8 8 8 7 Max 24-hr Avg 3.04114 2.83805 2.43740 2.85348 2.67140 3.0411 2.8380 2.4374 2.8535 2.6714 Receptor 294 294 117 294 85 294 294 117 294 85 Julian Day 38 5 83 75 16 38 5 83 75 16 No. of Calms 4 6 0 7 5 4 6 0 7 5 2nd Max 24-hr Avg 2.93632 2.56604 2.22876 2.45291 2.51026 2.9363 2.5660 2.2288 2.4529 2.5103 Receptor 117 294 294 294 294 117 294 294 294 294 Julian Day 37 32 27 11 6 37 32 27 11 6 No. of Calms 0 0 6 1 5 0 0 6 1 5 Max Annual Avg 0.97561 0.95755 0.88528 0.83420 0.95140 0.9756 0.9576 0.8853 0.8342 0.9514 Receptor 294 294 294 294 294 294 294 294 294 294 No. of Calms 658 966 902 867 1037 658 966 902 867 1037
Max 5-yr Qtr 24-hr 2.69811 Q1 2.6981 Q1
Receptor 294 294
Max 5-yr Avg 0.92081 0.9209
Receptor 294 294 No. of Calms 4430 4430
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NON-REGULATORY OPTION FOR USING AERMET METEOROLOGY
The meteorology utilized by CAL3QHCR in the dispersion calculations are: wind vector
(direction toward which it travels, in degrees), wind speed (in m/s), Pasquill atmospheric stability
class, and rural and urban mixing heights (in m). The processing of surface and upper air
measurements into a meteorological data file compatible with the CAL3QHCR model for
regulatory applications is typically completed using the Meteorological Processor for Regulatory
Models (MPRM). However, AERMET supplies meteorology that can be used to establish the
parameters required for CAL3QHCR dispersion calculations, either directly or indirectly.
AERMET provides the hourly wind direction (direction from which it originates), which
is directly related to the wind vector (i.e., the two parameters are 180º out of phase). AERMET
directly gives the hourly wind speed (in m/s).
The hourly Monin-Obukhov length (L, in m) and the surface roughness length (zo, in cm)
furnished by AERMET are used to compute the Pasquill atmospheric stability class required by
CAL3QHCR based on a relationship established by Golder (12). Golder’s relationship has been
implemented in EPA’s AERMOD (5), CALPUFF (13) and CTDMPLUS (14) models as depicted
in Figure 1. The subroutine from these EPA models is incorporated in the CAL3QHCR model
and is the basis for determining Pasquill atmospheric stability class as a function of L and zo
from AERMET.
FIGURE 6 Characterizing Pasquill Atmospheric Stability Class.
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The mixing heights required by CAL3QHCR are taken from the convective and
mechanical mixing heights supplied by AERMET. The rural mixing height for the convective
boundary layer (i.e., L < 0 m) is taken to be the larger of the convective mixing height and the
mechanical mixing height. Whereas, in the stable boundary layer (i.e., L ≥ 0 m), the rural
mixing height is based exclusively on the mechanical mixing height. For urban areas, the mixing
height is computed accounting for a convective boundary layer, which can form during the
nighttime when stable air from a rural area flows onto a warmer urban surface – the so-called
urban heat island effect. Adjustments are made to a reference boundary layer height of 400 m
corresponding a reference city population of 2,000,000, i.e., zuc = 400 m (P / 2,000,000)1/4 where
zuc is the nocturnal urban boundary layer height due to convective effects alone and P is the city
population.
Unlike data files produced with MPRM, an AERMET meteorological data file may
contain missing parameters. A routine was added to CAL3QHCR to identify critical missing
data, including wind vector, wind speed, and atmospheric stability. An hourly record with a
critical missing value is identified as a calm wind so that it is excluded from the concentration
computations.
Limited testing on the non-regulatory option for using AERMET meteorology has been
conducted, comparing a meteorological data set processed with MPRM and with AERMET for a
single case. The maximum 5-year average high quarterly 24-hour PM2.5 concentrations obtained
were 3.09 µg/m3 using MPRM meteorology versus 3.07 µg/m3 using AERMET meteorology at
different receptors. The maximum 5-year average annual PM2.5 concentrations obtained were
1.16 µg/m3 using MPRM meteorology versus 1.11 µg/m3 using AERMET meteorology at
different receptors.
NON-REGULATORY OPTION FOR USING AERMOD DISPERSION COEFFICIENTS
The horizontal (σy, in m) and vertical (σz, in m) dispersion coefficients employed in the
CAL3QHCR model are based on an extrapolation over downwind distances from the edge of a
turbulent mixing zone and 10 km. The initial values are calculated as a function of the mixing
zone residence time based on the General Motors sulfate experiments (15). Values at 10 km are
based on the original Pasquill-Gifford dispersion curves (16,17) for six Pasquill atmospheric
stability categories.
In contrast, AERMOD provides for a continuous measure of atmospheric stability based
on an energy balance in the planetary boundary layer. The AERMOD formulation (18) for
computing continuous σy and σz values at 10 km was incorporated into the CAL3QHCR model,
which can be used as a non-regulatory option. The dispersion coefficients computed by the
AERMOD formulation are adjusted for a specific averaging time according to the procedures of
the CAL3QHCR model. Since the AERMOD formulation accounts for the effects of surface
roughness length in the computation of σy and σz values, the adjustment for zo based on the
CAL3QHCR procedure is not made.
Testing on the non-regulatory option for using AERMOD dispersion coefficients has not
progressed sufficiently for reporting results.
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SUMMARY
Improvements have been made to the CAL3QHCR model to greatly enhance its applicability for
highway air quality analysis. And all improvements were made without affecting the
concentration estimates produced by the model.
The management of input files have been significantly streamlined, requiring a single
input data file along with a single meteorological data file to complete a simulation with 5 years
of meteorology. Contrast this to what is required by the U.S. EPA regulatory version of the
model, which requires a total of 60 files – 20 input data files (4 quarterly files for each of 5
years); 20 meteorological data files; and 20 control files.
The management of output files has similarly been streamlined, producing a single
descriptive output file, ETS file, and message file along with two post files and plot files. The
output files simplify the process of completing design value computations for project-level
transportation conformity analyses. Contrast this to what is produced by the EPA regulatory
version of the model, which totals 100 files – 20 descriptive output files, 20 et1 files, 20 et2 files,
20 message files, and 20 plot files.
Case studies are in progress to gain insights into the concentration predictions produced
by the non-regulatory options added to the model, including comparisons of measured versus
predicted concentrations. Work is also underway to incorporate the updated model into CAL3i,
the graphical user interface created by the Federal Highway Administration for the CAL3 series
of models.
ACKNOWLEDGEMENTS
Revisions to the CAL3QHCR code as described were completed by the author while employed
by the U.S. Department of Transportation, Federal Highway Administration, Resource Center.
The source code and executable program may the obtained from the author or downloaded from
the Transportation & Air Quality Committee (ADC20) of the Transportation Research Board
webpage (http://www.trbairquality.org).
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TRB 2014 Annual Meeting Paper revised from original submittal.
Michael Claggett 18
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http://www.epa.gov/ttn/scram/7thconf/aermod/aermod_mfd.pdf.
TRB 2014 Annual Meeting Paper revised from original submittal.