### CHAPTER 4
REGIONAL MODELING AND EVALUATIONMATES III Final Report

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## Chapter 4. Regional Mo deling and Evaluation

4.1 Introduction

Regional air quality modeling is used to determin e the concentration impact in time and space to the community due to emissions from a single or group of known toxic compounds and
emissions sources. The model simulated conc entration contours of toxic compounds are translated into a pattern of health risk based upon compound potency risk factors. The regional modeling provides a mechanism to disperse the em issions from a variety of source categories as
well as individual sources to estimate a mass c onsistent impact throughout the modeling domain. This analysis complements the data analytical techniques used to assess concentration and risk from the data acquired at the fixed monitoring sites.

Several comments received from reviewers of th e Draft MATES III report were directed at the regional modeling analysis and eval uation. The key areas addressed:

• The need for a direct comparison between th e regional modeling analyses generated for both MATES II and MATES III;

• The simulation performance elemental carbon (EC 2.5 ) compared with observations measured during the MATES III monitoring program; and

• The adequacy of the comparison of simulated risk to risk calculated based on monitored
data at the MATES III sites.

Several additional comments suggested modifica tions to the modeling assumptions including model configuration and specific emissions allocation. These included suggestions to:

• Modify (increase) the number of layers in the model domain;

• Evaluate alternate methodologies to cal culate vertical dispersion; and

• Review the emissions inventory in partic ular, the percentage apportionment of EC emissions released from ships.

The regional modeling analysis and evaluation presented in this document attempts to answer the key issues and suggestions identified through the review process. Most noteworthy, this document presents a newly-generated recreation of the MATES II modeling analysis that is consistent in model applica tion, inventory development, a nd modeling assumptions to the MATES III analysis described in the following sections.

For MATES III, the Comprehensive Air Quality Mode l with Extensions (CAMx) enhanced with a reactive tracer modeling cap ability (RTRAC) (Environ, 20 06) provided the dispersion modeling platform and chemistry used to simula te annual impacts of both gaseous and aerosol toxic compounds in the Basin. The version of th e RTRAC “probing tool” in CAMx used in theMATES III Final Report

modeling simulations includes an ai r toxics chemistry module that is used to treat the formation
and destruction of reactiv e air toxic compounds.

Modeling was conducted on a domain that encompa ssed the Basin and the coastal shipping lanes
located in the Southern Californi a Bight portions of the Basin using a grid size of two-squared kilometers. (Figure 4-1 depict s the MATES III modeling domain. The shaded portion of the grid area represents the extension of the domain beyond that used for MATES II). An updated version of the 2007 AQMP emissions inventory for model year 2005, which included detailed source profiles of air toxic sources, provided mob ile and stationary source input for the MATES
III CAMx RTRAC simulations. An additional b ack-cast of the 2007 AQMP emissions inventory was generated for 1998 to project emissions for use in the new simulation covering the MATES II monitoring period.

Figure 4-1 MATES III Modeling Domain. (Shaded area highlights the grid extens ion to the MATES II modeling domain).

Grid-based, hourly meteorological fields generated from the MM5 (PSU/NCAR 2004) mesoscale meteorological model using four dimens ional data assimilation, and National Weather

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Service model initializations for April 1998 th rough March 1999 and all days in 2005 provided the dispersion profile for the simulations.

4.2 Background

In the MATES II analysis, the Urban Airshed M odel with TOX (UAMTOX) chemistry was used
to simulate the advection and accumulation of toxic compound emissions throughout the Basin. UAMTOX was simulated for a protracted two-square d kilometer grid domain that overlaid the Basin. The analysis relied on the 1998 emissions projection from the 1997 AQMP and meteorological data fields for 1997-98 generated from objective analysis using a diagnostic wind
model. These tools were consistent w ith those used in both the 1997 and 2003 AQMP
attainment demonstrations.

Peer review of the 2003 AQMP mo deling strongly suggested th at future AQMP attainment
demonstrations utilize more state-of-the-scien ces tools that utilize updated chemistry modules, improved dispersion algorithms and mass consiste nt meteorological data. The recommendations were placed in action for the 2007 AQMP where th e dispersion platform moved from UAM to CAMx and the diagnostic wind meteorological model was replaced by MM5 prognostic model. CAMx, coupled with MM5 input using the “one atmosphere” gaseous and particulate chemistry, was used to simulate both episodic oz one and annual concentrations of PM 2.5

.

4.3 MATES III vs. MATES II: Key Modeling Assumptions

The MATES II modeling analysis was conducted using the UAM dispersion platform and the TOX chemistry package. The UAMTOX model wa s simulated using diagnostic meteorological model output and 1999 emissions data. At th e time when the MATES II simulations were conducted, UAM was considered a recommended disp ersion platform by U.S. EPA through their modeling guidance documents. The TOX chemistry package was one of a select few chemistry packages available for consideration in the analysis.

The MATES III simulations were conducted using the contemporary CAMx – MM5 coupled with the RTRAC chemistry. The decision to move away from UAMTOX for the current analysis was twofold: (1) to build upon the advances ga ined in the 2007 AQMP in annual particulate modeling using the pe er recommended state-of-the-sci ence modeling tools, and (2) to provide analysis consiste ncy with the 2007 AQMP PM 2.5 attainment demonstrat ion. (Note: the regional modeling analysis presented in this fina l document differs from that presented in the
draft to account for modifications made to mode ling assumptions, most notably the use of a landuse based vertical dispersion al gorithm and changes in EC shi pping emissions allocations in response to comments recei ved from reviewers).

It is difficult to fully assess the impact caused by the shift in modeling platforms and chemistry modules. Table 4-1 summarizes the major differences in the toxic modeling between the final MATES III and MATES II analyses. For example, MM5 model meteorological fields, including
wind characterization and estimation of vertical di ffusion, differ significantly from those created using diagnostic approaches and can greatly alter dispersion patterns throughout the modeling

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domain. Changes to emissions estimation assu mptions add to the uncertainty of a direct comparison of model simulations.

Table 4-1 Summary Comparison of Key Modeling Considerations Between
MATES III and MATES II

Parameter MATES III and 1998-99 Backcast MATES II

Model Platform / Chemistry CAMx RTRAC UAMTOX

Meteorology Model /Layers MM5 Prognostic: 29 layers/CAMx: 8 layers Diagnostic Wind Model / UAMTOX: 5 layers

Vertical Diffusion Blackadar PBL to determine grid-layer specific vertical diffusivity Hourly grid specified mixing height

On-Road Truck
Emissions Caltrans/SCAG Truck Model Used passenger vehicle pattern

Shipping Emissions Stack Height Emissions spread through layers 1 and 2 Emissions released in layer 1 (variable size) Emissions Inventory 2005 Projection from 2002 (2007 AQMP) 1998 Projection from 1997 (2003 AQMP)

Mobile Emissions EMFAC2007 EMFAC7G

To remedy this problem, this analysis provide s a newly-generated set of regional modeling simulations for the MATES II monitoring period using the CAMx – MM5 coupled with the RTRAC chemistry, 1999 back-cast emissions and newly generated 1998-99 meteorological
fields to facilitate a direct air quality and risk comparison between MATES II and MATES III. Development of the new simulations follow the sa me set of assumptions and model applications (where possible) as for the final MATES III analysis.

Three changes to emissions data preparation were implemented in the MATES III modeling. First, emissions from vessels in the shipping lanes were assumed emitted into the first two vertical modeling layers to better estimate plum e rise from the hot stack emissions. Combined stack heights and plume rise for typical ocean -going (deep draft) vessels extend above 36 and below 73 meters (WRAP, 2007). MATES II held sh ipping emissions in the first vertical UAM layer.

Second, the diesel particulate emissions profile for marine vessels and ocean-going vessels using diesel engines was changed to reflect a lower pe rcentage of elemental carbon contribution to the total mass. The initial profile used in the draft MATES III modeling simulations (as well as MATES II analysis) was characteristic of an on-ro ad diesel truck profile where elemental carbon fraction accounted for more than 20% of the pa rticulate mass. The revised analyses used a stationary source large diesel engi ne profile (which is assumed to be more consistent with the large engines operating on ships) that allocated the elemental carbon fraction at approximately

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6% of the total mass of diesel emissions. The total diesel mass emissions from this source category were not impacted by the revision.

The third modification impacted the distribution of truck movement throughout the Basin. At the time of MATES II, no heavy-duty truck move ment profile was available to characterize the
truck distribution and travel on fr eeways, arterial and major str eets. Truck travel was assigned the travel model characteristics designated for light-duty passenger vehicle travel. MATES III directly incorporated the out put of the heavy-duty truck demand model to provide a more
realistic characterization of wee kday travel. Weekend travel was assigned the same routes but at substantially lowered demand.

4.4 Modeling Results

CAMx RTRAC regional modeling wa s conducted using MM5 meteorol ogical data and projected
emissions data for 2005 to simulate annual av erage concentrations of 19 key compounds measured as part of the MATES III monito ring program. Simulated annual average concentrations plots for the four toxic compounds that contributed the greatest risk throughout the domain (diesel particulate, benzene, 1,3-butad iene and formaldehyde) are depicted in Figures 4-2 through 4-5.

Figure 4-2 depicts the projected annual average c oncentration distribution of diesel particulates in the Basin. The highest concentration (10.8 μ g/m 3 ) was simulated to occur in the grid cells around the Ports of Los Angeles and Long Beach. A secondary maximum occurs in the Central Los Angeles area extending southeast loosely following the Interstate 5 Corridor. In general, the distribution of diesel pa rticulates is aligned with the transp ortation corridors including freeways, major arterials and rail right-of-ways. Figures 4-3 and 4-4 provide the distributions of benzene and 1,3-butadiene respectively whereby the toxi c compounds are almost uniformly distributed throughout the Basin (reflecting pa tterns of light-duty fuel consumption). The formaldehyde profile shown in Figure 4-5 depi cts higher concentrations in th e heavily traveled western and central Basin, with additional hot spots in the downwind areas of the Basin that are impacted by higher levels of ozone formation (S anta Clarita and Crestline).

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Figure 4-2 Annual Average Concentration Pattern for Diesel PM 2.5

Figure 4-3 Annual Average Concentrat ion Pattern for Benzene

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Figure 4-4 Annual Average Concentration Pattern for 1,3-Butadiene

Figure 4-5 Annual Average Concentration Pattern for Total Formaldehyde

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Table 4-2 provides a summary of the model perfo rmance to recreate measured annual average concentrations. For this comparison, the monitored data for six stations are combined to provide an estimate of average Basin-wide conditions for the two sampling pe riods: 2005 and 1998-99. Two stations in 2005 (Huntington Park and Pico Rivera) did not have complete measurement records for the full 12 months and were excluded from the analysis. Similarly, complete measurements for Compton and West Long B each were not available for 1998-99. CAMx RTRAC simulated pollutant concentr ations for the six stations that have complete data for the two measurement periods were calculated from th e grid data using the distance-weighted ninecell average. No direct measurements of PM 2.5 diesel were available for comparison to simulate annual average concentrations. However, estimate s of diesel particulate concentrations based on Chemical Mass Balance (CMB) analysis us ing ambient measured elemental carbon
concentrations are discussed later. Measured co ncentrations of naphthale ne were available for West Long Beach, Central Los Angeles, and Rubidoux. Each of the four counties is represented by at least one station. The six stations averag e measured and simulated concentrations provide an estimate of the regional prof ile but with a bias toward impact s to the coastal communities in the heavily transited areas of the Basin. Moreove r, the assessment provides a direct comparison for model performance evaluation.

Table 4-2 Compounds Simulated and Measured: Six-St ation Annual Average Concentrations 2005 MATES III and 1998-99 CAMx RTRAC Analyses

2005 MATES III 1998-99 MATES II (CAMx RTRAC Simulation) Compound Units Measured
Annual Average Simulated
Annual Average Measured
Annual Average Simulated Annual Average

EC 2.5 μ g/m 3 1.78 1.58 N/A N/A

EC 10 μ g/m 3 2.04 2.05 3.01 2.03
Cr 6 (TSP) η g/m 3 0.22 0.21 0.18 0.17

As (2.5) η g/m 3 0.5 0.92 N/A N/A
As (TSP) η g/m 3 0.68 2.46 1.79 3.00
Cd (2.5) η g/m 3 1.46 0.49 N/A N/A
Cd (TSP) η g/m 3 1.56 0.78 6.57 1.00
Ni (2.5)) η g/m 3 3.93 3.65 N/A N/A
Ni (TSP) η g/m 3 4.44 5.82 7.51 6.83
Pb (2.5 ) η g/m 3 5.41 2.60 N/A N/A
Pb (TSP) η g/m 3 10.64 8.68 22.72 10.00

Benzene ppb 0.53 0.52 0.97 0.75 Perchloroethylene ppb 0.06 0.09 0.27 0.18 p-Dichlorobenzene ppb 0.03 0.08 0.12 0.06 Methylene Chloride ppb 0.35 0.32 0.70 0.54

Trichloroethylene ppb 0.03 0.03 0.10 0.05

1,3-Butadiene ppb 0.1 0.09 0.29 0.13 Formaldehyde ppb 3.61 3.26 4.00 3.75 Acetaldehyde ppb 1.64 1.12 1.81 1.26 Naphthalene ppb 0.02* 0.01 N/A 0.02 * Three station average

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In general, 2005 model simulated particulate EC 2.5 , EC 10 , hexavalent chromium and PM 2.5 nickel average annual toxic compound concentrations comp ared well with the measured annual average values. The majority of gaseous components were well-simulated with the sole exception of acetaldehyde which is underpredicted. Arsenic a nd TSP lead exhibit the greatest tendency for overprediction. Cadmium and PM 2.5 lead concentrations tend to be underpredicted. In general, the concentrations of the gaseous compounds are closely recreated.

For 1998-99, there exists a gene ral tendency for underprediction. Hexavalent chromium and nickel average annual toxic compound concentrati ons are exceptions that are closely matched to
observations. Aside from the uncertainties as sociated with the modeling analyses, some uncertainty in prediction accuracy is introduced into the analysis through the measurement and analysis programs. The 1998-99 data samples were measured and analyzed by different agencies (AQMD and ARB) and their laboratories. In addition, the substitution of one-half level of
detection for data measured below the detection lim it also adds to the uncertainty in the analysis.

Simulated annual average EC 2.5 was the compound used to assess overall model performance for the 2005 MATES III period at the eight sites having a full year’s sampling. The analysis used annual average EC 2.5 model performance to provide c onsistency with the 2007 AQMP annual average PM 2.5 attainment demonstration modeling assessment. While the 2007 EC 2.5 AQMP modeling was conducted on a coarser grid (5 kilo meter squared), it was expected that the summary performance of the CAMx RTRAC 200 5 MATES III simulation should be consistent
but not identical. Table 4-3 summarizes the 2005 MATES III EC 2.5 model performance.

EPA guidance (U.S. EPA, 2006) recommends ev aluating particulate modeling performance using measures of prediction bias and error. An additional useful tool is prediction accuracy (PA) measured as the percentage difference between the mean annual observed and simulated

EC 2.5 concentrations. PA goals of ±20% for ozone and ±30% for individual components of

PM 2.5 or PM 10 have been used to assess simulation perf ormance in previous modeling attainment demonstrations. PA at seven of the eight MATES III sites meet the PM 2.5 goal, with only Burbank exhibiting a large degree (50%) of underpre diction of the annual av erage concentration. Of the remaining sites, Inland Valley San Bernardino and Rubidoux are underpredicted by 19 and 22%, respectively, and North Long Beach is ove rpredicted by 22%. All other sites PA falls
within ±10 % of observations.

Analysis of the poor performance at Burbank revo lves around the inability of the meteorological model to exactly recreate observed winds in an area of complex terrain where the winds are required to bifurcate and revers e directions in a short distan ce. Winds from the southeast transport mobile source emissions from the 101 Freeway, Interstate 5, a nd a major leg of the
north and southbound commuter and cargo rail systems directly at the Burbank air monitoring
site. While the MM5 wind fields do an admirabl e job of turning the sea breeze northward in the immediate Burbank area, the simulated resultant flow is from the south and only captures a portion of the mobile source impact. In addition, the upwind grid cells adjacent to the south of the Burbank grid include the wild land open spac e of Griffith Park where emissions are limited. (A detailed discussion of model perfor mance is presented in Appendix IX).

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Table 4-3
MATES III 2005 EC 2.5 Model Performance

Location EC 2.5 Observed ( μ g/m 3 ) Modeled
Observed

Days ( μ g/m 3 ) Prediction Accuracy Mean
Bias ( μ g/m 3 ) Mean

Error ( μ g/m 3 ) Normalized
Mean Bias

( μ g/m 3 ) Normalized

Mean Error

( μ g/m 3 )

Anaheim 1.41 1.35 -4 -0.06 0.54 0.39 0.61

Burbank 2.04 1.03 -50 -1.02 1.11 -0.31 0.48
Compton 1.76 1.88 7 0.12 0.61 0.39 0.52 Inland Valley San
Bernardino. 2.18 1.77 -19 -0.41 0.91 0.09 0.56 Long Beach 1. 40 1.71 21 0.30 0.61 0.54 0.64

Central L.A. 1.93 2.04 6 0.11 0.76 0.39 0.58

Rubidoux 1.69 1.32 -22 -0.38 0.74 0.09 0.58 West Long Beach 2.07 2.14 3 0.07 0.79 0.33 0.53

All Stations 1.86 1.70 -9 -0.17 0.77 0.23 0.54

4.5 Estimation of Risk

Figure 4-6 depicts the distribution of risk estimated from the predicted annual average concentrations of the key toxic compounds. Risk is calculated for each grid cell as follows:

Risk i,j = Σ Concentration i,j,k X Risk Factor i,j,k

Where i,j is the grid cell (easting, northi ng) and k is the toxic compound.

The grid cell having the maximum simulated ri sk of 3,693 was located in the Ports of Los Angeles and Long Beach. More spec ifically, the grids having the top 25 estimated risk values in
2005 were located in cells around th e ports area. The cell having the highest risk outside of the port area occurred in South Los Angeles as part of a cluster of grids that extended from Central Los Angeles to the southeast following Interstate-5. Other elevated areas included the eastern Basin near the communities of Colton, Inland Va lley San Bernardino, and San Bernardino. As with the MATES II analysis, areas projected to have higher risk followed transportation corridors, including freeways and railways.

Figure 4-7 provides the CAMx RT RAC simulated air toxics risk for the 1998-99 period (using back-cast 1998 emissions and 1998-99 MM5 generated meteorological data fields). Figure 4-8 depicts the 1998-99 to 2005 change in risk estimated from the CAMx RTRAC simulations. The greatest increase in risk occurred in the port area. Overall, air toxics risk improves to varying levels in most of the Basin with the exceptions of the areas directly dow nwind of the Ports and those areas heavily impacted by ac tivities associated with goods movement. Risk increases of
more than 800 in a million between the two periods were noted in the immediate areas encompassing the ports.

The 2005 Basin average population- weighted risk summed for th e toxic components yielded a cancer risk of 853 in a million. (The Basin aver age risk included all populated over land cells

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that reside within the Basin portion of the mode ling domain). The MATE S II Basin average risk was 981 per million as determined from the UAMTOX modeling analysis. However, when Basin population-weighted average risk is r ecalculated for the 1998- 99 MATES II period using CAMx RTRAC modeling platform the comparable Basin average risk is 931 per million. A direct comparison of Basin risk calculated using the CAMx RTRAC simulations between
MATES II and MATES III shows an 8% reduction. The 8% reduction in Basin risk can be attributed to several factors, most notably ch anges in emissions and spatial allocation between 1998 and 2005. While weather profiles between the two monitoring periods varied, no appreciable difference was observed in th e meteorological dispersion potential.

Regional risk from non-diesel sources (Figure 4-9) is also uniformly distributed throughout the Basin with values typically ranging from 100 to 300 in one million. Several elevated grid cells are apparent with risk estimated upwards of 400 in one million in the coastal plain encompassing Los Angeles International Airpor t and the heavily indus trialized areas south of Downtown Los Angeles. Selected elevated grid cells are also evident in the east Basin with values of up to 1,000
in one million.

Figure 4-10 provides a focused 2005 estimated air toxics risk in the Po rts area. Table 4-4 provides a summary risk estimated for the Basin, for the Ports area, and for the Basin excluding the Ports area. For this assessment, the Port s area includes the populated cells roughly bounded by the Interstate 405 to the north, San Pedro to the west, Balboa Harbor to the east and Pt. Fermin to the south. The 2005 average population-we ighted air toxics risk in the Ports area (as defined above) was 1,415 in one million. The Basi n average population-weight ed air toxics risk, excluding the grid cells in the Ports area, valued 816 in one million. (It is important to note that the downwind impacts resulting from Port area activities are reflected in the toxics risk estimates for the grid cells categorized as “Basin minus Po rts”). A similar calculation based on the CAMx
RTRAC simulations for 1998-99 indicated that the Po rts area air toxics ri sk was 1,208; and the Basin, minus the Ports area, was 912 in one m illion. Overall, the Ports area experienced an approximate 17% increase in risk, while the aver age population-weighted risk in other areas of the Basin decreased by about 11%.

As a sensitivity analysis, simulations were ge nerated to examine the hypothesis “what would the Basin toxics risk profile in 2005 be if no growth occurred in the goods movement sector from 1998?” To attempt to answer this question, hea vy-duty truck transport, shipping, port and rail operation activity levels associated with goods move ment were held at 1998 levels. The impacts of fleet turnover and control measure implemen tation were allowed to go forward through 2005 to develop the hypothetical emission s inventory. The results of the sensitivity test indicated that the Ports area, Basin, and Basin excluding the po rts areas would experience lower toxic risk levels by 6.2%, 14.8%, and 15.46% respectively.

4-11MATES IIIFinal Report4-12Figure 4-62005 MATES III CAMx RTRAC Simulated Air Toxic RiskMATES IIIFinal ReportToFigure 4-71998-99 MATES II CAMx RTRAC Simulated Air Toxic Risk4-13MATES IIIFinal ReportFigure 4-8Change in CAMx RTRAC Simulated Air Toxics Risk (per million) fromthe 1998-99 to 2005(using back-cast 1998 emissions and 1998-99 MM5generated meteorological data fields)4-14MATES IIIFinal ReportFigure 4-9MATES III 2005 Simulated Air Toxic Risk-No Diesel4-15MATES III Final Report

4-16 Figure 4-10
2005 Ports Area MATES III Simulated Air Toxic Risk

Table 4-4
Basin and Port Area Po pulation-Weighted Risk

MATES III MATES II*

Region 2005 Population Average
Risk (Per Million) 1998 Population Average
Risk (Per Million) Average Percentage Change in
Risk

Basin 15,662,620 853 14,404,993 931 -8

Ports Area 959,761 1,415 911,834 1207 17 Basin Excluding

Ports Area 14,702,859 816 13,493,159 912 -11

* CAMx RTRAC SimulationsMATES III Final Report

Figures 4-11 through 4-14 provide close-up depictions of risk to Central Los Angeles, Mira Loma, Colton, Central Orange County, and West Los Angeles areas, respectively.

Table 4-5 provides the county break down of air toxics risk to the affected population. As presented in the spatial distri bution, Los Angeles County bears th e greatest average risk at 951 per one million person population. Orange County has the second highest number of projected risk at 781 per one million person population. Risk in the Eastern Basin is lower. The estimated
risk for San Bernardino is 712 per million, and Riverside was estimated to have the lowest population-weighted risk at 485. It should be noted that these are county-wide averages, and individual communities could have higher risks th an the average if they are near emissions sources, such as railyards or intermodal facilities.

Comparison of the county-wide population-weight ed risk shows that the greatest reduction occurred in Los Angeles County. Reductions in emissions from mobile sources including benzene, 1,3-butadiene, and dies el particulate have contributed to the improved county-wide risk. A similar profile is evident in Orange County. Despite across-the-board improvements in measured toxic air quality from MATES II (with th e sole exception of hexavalent chromium at Rubidoux), population growth in the east Basin a nd associated increases in mobile source
emissions has resulted in a nominal increase in population-weighted risk for Riverside County. Similarly, San Bernardino County risk levels improved only marginally.

Table 4-5 County-Wide Populatio n-Weighted Risk

MATES III MATES II* Region

2005 Population Average
Risk (Per Million) 1998 Population Average
Risk (Per Million) Average Percentage Change in
Risk

Los Angeles 9,887,127 951 9,305,726 1,047 -9 Orange 2,764,620 781 2,579,794 833 -6
Riverside 1,548,031 485 1,249,554 478 2
San Bernardino 1,462,842 712 1,269,919 725 -2

SCAB 15,662,620 853 14,404,993 931 -8

* CAMx RTRAC Simulations

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Figure 4-11 2005 Central Los Angeles MATES III Simulated Air Toxic Risk

Figure 4-12
2005 Mira Loma/Colton MATES I II Simulated Air Toxic Risk

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Figure 4-13 2005 Central Orange County MATES III Simulated Air Toxic Risk

Figure 4-14 2005 West Los Angeles MATES I II Simulated Air Toxic Risk

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Table 4-6 provides the Basin average breakdown of risk associated with each of the key compounds simulated in the analysis. Diesel pa rticulate ranked highest as the toxic compound contributing to the overall risk from air toxi cs to the population. The next three highest contributors included benzene, 1,3-buta diene and hexavalent chromium.

Table 4-6
2005 MATES III Risk from Simulated I ndividual Toxic Air Contaminants

Toxic Compound Risk Factor ( μ g/m 3 ) Peak
Annual Average
Concentration Population Weighted

Annual Average
Concentration Units Cumulative
Risk (per million) %
Contribution

Diesel 3.00E-04 11.70 2.35 μ g/m 3 703.76 82.5

Benzene 2.90E-05 1.15 0.48 ppb 44.53 5.2

1,3- Butadiene 1.70E-04 2.32 0.081 ppb 30.45 3.6
Hexavalent Chromium

6 1.50E-01 0.003 0.00016 μ g/m 3 23.41 2.7 Primary Formaldehyde 6.00E-06 4.89 1.60 ppb 11.78 1.4 Secondary Formaldehyde 6.00E-06 1.60 1.30 ppb 9.61 1.1

Arsenic 3.30E-03 0.022 0.0024 μ g/m 3 7.97 0.9
p-Dichlorobenzene 1.10E-05 0.208 0.076 ppb 5.01 0.6 Secondary Acetaldehyde 2.70E-06 0.766 0.67 ppb 3.25 0.4
Perchloroethylene 5.90E-06 0.370 0.92 ppb 3.67 0.4

Napthalene 3.40E-05 0.046 0.017 ppb 3.10 0.4

Cadmium 4.20E-03 0.009 0.00054 μ g/m 3 2.28 0.2
Primary Acetaldehyde 2.70E-06 0.917 0.35 ppb 1.72 0.2
Methylene Chloride 1.00E-06 1.062 0.29 ppb 1.02 0.1

Nickel 2.60E-04 0.298 0.0035 μ g/m 3 0.90 0.1
Trichloroethylene 2.00E-06 0.340 0.029 ppb 0.31 < 0.1

Lead 1.20E-05 0.104 0.0075 μ g/m 3 0.09 <0.1

Table 4-7 provides the simulated air toxics risk at each of the eight stati ons (evaluated in Table 4-2) for the three main toxic compounds and the remaining aggregate based on the regional modeling. Risk is calculated using the predicte d concentrations of each toxic component for the specific monitoring station location (based on a ni ne-cell weighted average concentration). The summary also provides the comparison between si mulated average risk for the eight stations

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combined and the average risk calculated us ing the annual toxic compound measurements and
the estimated diesel concentrations at those sites.

Table 4-7 Comparison of Network Averaged CAM x RTRAC 2005 Modeled Risk to Measured Risk at the Eight MATES III Sites
2005 MATES III CAMX RTRAC Simulation

Location Benzene 1,3-
Butadiene Others Diesel Total

Anaheim 47 31 75 900 1,054
Burbank 44 25 64 613 746 Compton 52 54 94 950 1,150 Inland Valley San Bernardino 41 25 121 734 922 North Long Beach 53 36 84 1,282 1,455 Central Los Angeles 64 47 115 1,256 1,482
Rubidoux 42 33 70 700 845 West Long Beach 55 30 86 1,501 1,672 8-Station Average Modeled 50 35 89 992 1,166 8-Station MATES III Average Measured (EC 2.5 * 1.95 for Diesel) 53 34 83 1,070 1,240

8-Station Average Measured (with range of CMB Diesel risk ) 53 34 83 1,004

– 1,120 1,174 – 1,290

8-Station Average Measured (average of CMB Diesel risk ) 53 34 83 1,062 1,232

The highest simulated risk was estimated for West Long Beach followed by Los Angeles, North Long Beach, and Compton. The lowest modeled ri sk was simulated at Burbank. As previously discussed, simulation performance at Burbank show ed a tendency for underprediction; and this feature appears to be translated to the risk calculation.

The non-diesel portion of the simulated risk can be directly compared to ri sk calculated from the toxic compound measurements. Figure 4-15 presen ts a comparison of the model simulated and
measurement estimated non-diesel risk at each monitoring site, as well as the eight-station average. Simulated non-diesel risk is within 30% of measurements at all stations with the sole exception of Burbank. In general, there a ppears to be no geographical bias in model performance, and the simulated eight-station aver age risk is essentially equal to the risk
estimated from the measurements.

Simulated total risk includes the contribution of di esel particulates and, ta ken as an eight-station average, the modeled risk 1,166 in a million. The eight-station average simulated risk is approximately 6% lower than the risk cal culated from the measured toxic compound concentrations and the estimates of diesel concentrations using the emissions based factor (1.95) applied to the EC 2.5 average concentration. When the mode l simulated risk is compared to the measurement calculated risk, including the range of CMB estimated diesel concentrations, the

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eight-station average risk was nominally less th an the lower projection of the range based on measurement data. The eight-station simulated risk based on the CAMx RTRAC analyses was approximately 10% lower than th e average of the CMB estimated diesel risk based on the two source profiles.

4.6 Evaluation

The population-weighted average Basin air toxics risk (853 per million) simulated using CAMx RTRAC for the 2005 MATES III period was estimated to be 8% lower than estimated (931 in a million) for 1998-99 when the same modeling plat forms and year specific meteorology are evaluated. This is loosely compared to a 17% reduction in average population-weighted risk (981) estimated for the 1998-99 MATES II anal ysis using the UAMTOX modeling platform. The areas of the Basin having maximum risk con tinued to be the Ports of Los Angeles and Long Beach with a secondary maximu m occurring in an area starti ng in South Los Angeles and extending toward southeastern Los Angeles.

0 50 100 150 200 250 300

Anaheim Burbank Compton Inland Valley

S.B. North Long

Beach Los Angeles Rubidoux West Long

Beach 8-Station AverageRisk Per Million

Observed Estimated

Figure 4-15
2005 MATES III Simulated vs. Measured Concentrations for Non-Diesel Air Toxics Risk

The average simulated Basin air toxics risk fo r the 2005 MATES III data is 8% lower than the comparable average risk estimated for th e 1998 MATES II analysis. Using the 2007 AQMP inventory back-cast methodology, the percentage reduction in diesel mass emissions from 1998 to 2005 is approximately 5%. However, emissions reductions of benzene (36%), 1,3-butadiene (31%), arsenic (20%) and hexavalent chromium (85%) contribute greatly to the overall reduction in 2005 simulated risk. A general assessment of the observed meteorolog ical profile suggests that the two monitoring periods were co mparable in dispersion potential.

4-22MATES III Final Report

4-23 4.7 References

ENVIRON, Inc., 2008. CAMx User’s Guide Version 4.5 . ENVIRON. Novato, CA 94945

PSU/NCAR Mesoscale Model (MM5) 2004, http ://www.mmm.ucar.edu/mm5/mm5-home.html

WRAP, 2007, Western Regional Air Partnership, Technical Support System, Emissions Method, Offshore Emissions, http://vista.cira.colostate.edu/

U .S. EPA, 2006,” Guidance on Use of Modele d and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM 2.5 and Regional Haze NAAQS,” U.S. EPA, Office of Air Quality Planning and Standards, Emissions, Monitoring, and Analysis Division, Air Quality Modeling Group, Research Triang le Park, North Carolina, September, 2006