CRC Report No. A-34 - Coordinating Research Council

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April 2005 2.0 PHOTOCHEMICAL MODELING METHODOLOGY This section of the report describes how the photochemical grid modeling was performed to prepare synthetic air samples for receptor locations in the Los Angeles area. An overview of A- 34 study design was presented in Section 1. The procedures described below were developed in modeling protocol at the outset of the study. The modeling protocol was reviewed by CRC, but not by DRI since this would have revealed critical information. 2.1 MODELS, DOMAIN, EPISODE AND RECEPTORS The Comprehensive Air-quality Model with extensions (CAMx) photochemical modeling database for the August 3-7, 1997 Southern California Ozone Study (SCOS) episode was used for this study. This is the same database as was used in the CRC A-36-A1 Weekday/Weekend Proximate Modeling (Yarwood et al., 2002 and 2003a) and CRC A-38 EMFAC on-road vehicle emission factor model evaluation (Yarwood et al., 2003b) studies. The previous studies have found good model performance for ozone and ozone precursors in the Los Angeles are with this modeling system. Ambient Conditions During the SCOS Episode The August 3–7, 1997 ozone episode began with warm temperatures at the surface and aloft and weak pressure gradients directed offshore opposing onshore sea breezes. August 3 was the first model spin-up day and is not discussed. Ozone concentrations were relatively low on August 4 in most locations with the highest ozone occurring inland in the mountains and passes consistent with onshore flow. On August 5, temperatures increased reaching 29 °C at Los Angeles International Airport (LAX) and 49 °C at Palm Springs. The offshore pressure gradient increased in intensity and the episode maximum ozone concentration was 187 ppb at Riverside, consistent with continued weak onshore flow. By August 6, the offshore pressure gradients had weakened and inland temperatures cooled (43 °C at Palm Springs). The maximum ozone on August 6 occurred in the mountains at Crestline. On August 7, pressure gradients turned onshore and the onshore winds strengthened so that the highest ozone concentrations occurred far inland. The meteorological patterns during the August 3–7, 1997 period fit a typical pattern for Los Angeles ozone episodes. High ozone levels occurred because the period was relatively stagnant, tending to trap ozone and precursors within the Los Angeles basin. Models and Modeling Domain Photochemical ozone modeling for the August 3-7, 1997 SCOS period was performed with version 4.03 of the Comprehensive Air-quality Model with extensions (CAMx; ENVIRON, 2004). CAMx simulates the emission, dispersion, reaction, and removal of ozone precursors and ozone in a Eulerian (grid) framework. The modeling domain covered 65 by 40, 5-km grid cells as shown in Figure 2-1. This domain was selected to be consistent with past modeling for air quality management plans in the LA area (SCAQMD 1997, 1999). CAMx was run with 10 layers extending between a surface layer of 60 m and a model top at 4 km. H:\crca34-receptor\report\Final\sec2.doc 2-1
April 2005 Meteorological input data for CAMx were developed using the Penn State/NCAR Mesoscale Model, version 5 (MM5). The MM5 is a non-hydrostatic, prognostic meteorological model that simulates atmospheric properties based on fundamental equations, but also permits assimilation of observed data to nudge the simulated meteorological fields toward the data (Dudhia, 1993). MM5 was run with assimilation of SCOS measurement data assembled by the CARB (i.e., radar wind profiler upper-air data and surface site data) and Eta Data Analysis System data from the National Centers for Environmental Prediction (NOAA-ARL, 2002). The CAMx modeling grid was closely matched to the MM5 grid and, in particular, CAMx layer interfaces exactly matched MM5 layer interfaces to facilitate direct mapping of meteorological parameters from MM5 to CAMx. UTM Northing (km) 3850 3800 3750 3700 Pacific Ocean Kern County Los Angeles County Ventura Crestline County Van Nuys Diamond Bar LAX Hawthorn Lake Perris Long Beach Anaheim Orange County 300 350 400 450 500 550 600 UTM Easting (km) San Bernardino County Riverside County San Diego County 2600 m 2400 m 2200 m 2000 m 1800 m 1600 m 1400 m 1200 m 1000 m 800 m 600 m 400 m 200 m 0 m -200 m Figure 2-1. CAMx photochemical modeling domain showing terrain height (m) and receptor locations for the CMB analysis. Selection of a Photochemical Mechanism for the Host Model The photochemical mechanism for the host model is important because it provides the oxidant fields to chemically decay the PAMS species reactive tracers. CAMx supports both the CB4 (Gery et al., 1989) and SAPRC99 (Carter, 2000) chemical mechanisms. Emission inventories for the August 1997 SCOS episode are available for both the CB4 and SAPRC99 chemistry. The CB4 chemical mechanism was selected because, together with the other model inputs, it better replicates the observed ozone levels for the August SCOS episode than the SAPRC99 mechanism (Yarwood et al., 2003b). Reactive Tracers (RTRAC) for PAMS Species and Source Categories Atmospheric concentrations of specific PAMS species from specific source categories were modeled using a reactive tracer methodology (RTRAC) included in CAMx (ENVIRON, 2004). This methodology was developed and tested for modeling air toxics species in Los Angeles for H:\crca34-receptor\report\Final\sec2.doc 2-2
Page 1 and 2: International Corporation Air Scien
Page 3 and 4: April 2005 TABLE OF CONTENTS Page E
Page 5 and 6: April 2005 Table 4-1. Categories id
Page 7 and 8: April 2005 EXECUTIVE SUMMARY Recept
Page 9 and 10: April 2005 Comparing the performanc
Page 11 and 12: April 2005 90 12 Anaheim 80 10 Cr e
Page 13 and 14: April 2005 This assumption is a mat
Page 15 and 16: April 2005 dissimilar from the loca
Page 17 and 18: April 2005 1.0 INTRODUCTION 1.1 STU
Page 19: April 2005 1.4 OVERVIEW OF PROJECT
Page 23 and 24: April 2005 A-34 Num Short Name Full
Page 25 and 26: April 2005 Sunday 3-Aug-97 Monday 4
Page 27 and 28: April 2005 ARB ROG TOG ARB Profile
Page 29 and 30: April 2005 Industrial facilities fr
Page 31 and 32: April 2005 Figure 2-2. Comparison o
Page 33 and 34: April 2005 2.4 EXPERIMENTS FOR ROUN
Page 35 and 36: April 2005 Table 2-9. Source catego
Page 37 and 38: April 2005 Table 2-13. Replacement
Page 39 and 40: April 2005 from front to back is th
Page 41 and 42: April 2005 3. Set the average diese
Page 43 and 44: April 2005 Table 2-15. Model year d
Page 45 and 46: April 2005 Table 2-17. Fuel composi
Page 47 and 48: April 2005 3.0 RECEPTOR MODELING ME
Page 49 and 50: April 2005 Selection of Fitting Spe
Page 51 and 52: April 2005 samples. Spatial variati
Page 53 and 54: April 2005 • Removed ethane from
Page 55 and 56: April 2005 Table 3-2. Criteria for
Page 57 and 58: April 2005 Table 3-4 (continued). N
Page 59 and 60: April 2005 120 100 80 60 40 20 0 no
Page 61 and 62: April 2005 4.0 RESULTS This section
Page 63 and 64: April 2005 (c) Round 4: Experiment
Page 65 and 66: April 2005 emissions contributions,
Page 67 and 68: April 2005 reactivity and found CMB
Page 69 and 70: April 2005 (c) Round 4: Experiments
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April 2005 (a) 6:00am to 9:00am 80
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April 2005 (a) siteid Anaheim exp 1
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April 2005 influence CMB performanc
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April 2005 Round 3: Experiments 9-1
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April 2005 Comparison of Source Con
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April 2005 Table 4-2. Source catego
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April 2005 contributions being diff
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April 2005 to 2.4 over the A-34 sou
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April 2005 Experiment 1: Base Case
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April 2005 28. Spatial heterogeneit
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April 2005 composition derived from
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April 2005 species (CNG and LPG for
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April 2005 REFERENCES Allen, P. 200
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April 2005 Guenther, A., B. Baugh,
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APPENDIX A Supplemental Modeling Re
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SCC Description TOG %TOG Cumulative
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SCC Description TOG %TOG Cumulative
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ARB Profile Number TOG %Total % TOG
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A-34 Number SCC Code SCC Descriptio
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A-34 Number SCC Code SCC Descriptio
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Table A-4 (continued). A-34 Source
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Table A-5. Mean source profiles (PA
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Table A-5 (concluded). A-34 Source
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APPENDIX B CMB-Derived Source Contr
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SCE (ppbC) SCE (ppbC) 18 16 14 12 1
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SCE (ppbC) 14 12 10 8 6 4 2 0 6 5 C
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SCE (ppbC) 12 10 8 6 4 2 0 6 5 Cons
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SCE (ppbC) 10 9 8 7 6 5 4 3 2 1 0 6
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SCE (ppbC) 6 5 4 3 2 1 0 Consumer P
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SCE (ppbC) SCE (ppbC) SCE (ppbC) 4
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SCE (ppbC) SCE (ppbC) 12 10 8 6 4 2
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SCE (ppbC) SCE (ppbC) SCE (ppbC) 10
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SCE (ppbC) 9 8 7 6 5 4 3 2 1 0 12 1
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SCE (ppbC) SCE (ppbC) SCE (ppbC) SC
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SCE (ppbC) 6 5 4 3 2 1 0 Consumer P
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SCE (ppbC) 160 140 120 100 80 60 40
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Diamond Bar - Source Category 14 Di
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CRC Report No. A-34 - Coordinating Research Council

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