Final Report: Exposure Assessment and Airshed Modeling Applications in Support of SCPC and CHS Projects

EPA Grant Number: R827352C015
Subproject: this is subproject number 015 , established and managed by the Center Director under grant R827352
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Southern California Particle Center and Supersite
Center Director: Froines, John R.
Title: Exposure Assessment and Airshed Modeling Applications in Support of SCPC and CHS Projects
Investigators: Turco, Richard , Yu, Rong Chun , Winer, Arthur M. , Lurmann, Fred , Wu, Jun
Institution: University of California - Los Angeles
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

Topic C: Studies of the Effects of Varying Spatial and Temporal Patterns of Ambient Particulate Matter (PM) and Co-pollutants and Resulting Health Effects with Emphasis on the Role of Atmospheric Chemistry

Two overall objectives of this integrated modeling project were to utilize airshed model outputs as inputs to exposure assessment models designed to quantify long-term average exposure of subjects in the Children’s Health Study (CHS) to criteria pollutants; and assess population exposure to ambient naphthalene concentrations in Southern California. In the course of this research we also demonstrated significant problems with the accuracy of widely-used roadway networks and geocoded addresses. In addition, we developed methods for improvements in these important parameters, and also investigated environmental justice implications of traffic-related air pollution in Southern California.

Summary/Accomplishments (Outputs/Outcomes):

Airshed Modeling

The distributions of gaseous and particle-borne pollutants across the California South Coast Air Basin (SoCAB) were analyzed in support of the Southern California Particle Center and Supersite (SCPCS) assessments of regional human exposure, as summarized in the Exposure Assessments section below. The airshed modeling research centered on simulations carried out with the University of California-Los Angeles (UCLA) Surface Meteorology and Ozone Generation (SMOG) model, which was extended and tested for accuracy against monitoring and field data and shown to be accurate for criteria pollutants in the range of +25% to -35%, with larger variability for particulate components.

The principal objectives of the airshed research were to establish the regional distributions of specific pollutants for population exposure assessments, and provide information for exposure assessments associated with CHS. To meet our objectives, we characterized the spatial and temporal variations in the concentrations of ozone, trace metals, elemental carbon, certain polycyclic hydrocarbons and their photochemical byproducts, and related substances under a variety of conditions in the SoCAB.

Pollutant Distributions for Trace Metals and Elemental Carbon. Early work under this project considered airborne particles and their trace composition throughout the SoCAB, accounting for emission sources, microphysical processing, meteorological dispersion, sedimentation and deposition, and ventilation. The surface concentrations of zinc, lead, and up to a dozen other metals, as well as elemental carbon (EC), were simulated for a period corresponding to the Multiple Air Toxics Exposure Study (MATES II) field campaign. Comparisons showed the SMOG model yielding acceptable predictions. These results were the first that explicitly resolved temporal, spatial, and size variations in elemental carbon on a regional scale for exposure assessment.

Naphthalene and Naphthoquinones. Naphthalene is the most abundant of the polycyclic aromatic hydrocarbons (PAHs) in the SoCAB, and is found mainly in the gas-phase. A naphthalene photochemical mechanism was assembled for use in the SMOG model. The distributions of naphthalene and naphthoquinones were then calculated throughout the SoCAB for the first time. To verify mobile source emission factors for naphthalene, an experiment was organized through the SCPCS at the high-traffic Sepulveda tunnel near Los Angeles International Airport. The naphthalene-to-benzene mass ratio was measured in tunnel air samples. Because benzene emission factors are considered to be reliable, the new field data were used to cross-calibrate California Air Resources Board (CARB) naphthalene emission rates, which were found to be consistent with the tunnel data. A second experiment was carried out in Pasadena, which also yielded naphthalene-to-benzene mass ratios consistent with those predicted by the SMOG model. Naphthalene concentrations obtained using SMOG simulations were employed to calculate population exposure statistics, as discussed below.

CHS. To improve regional predictions of particulate pollutant distributions in support of the CHS exposure assessments, SMOG was updated using the South Coast Air Quality Management District’s 2003 Air Quality Management Plan inventories for CO, NOx, SOx, volatile organic compound (VOC), and PM emissions, along with the CARB EMFAC-2002 emission factors and 2001 transportation activity data developed by the Southern California Association of Governments. A module to compute secondary organic aerosol (SOA) production, and a biogenic emission database (CARB’s BEIGIS inventory), were also integrated into the SMOG model.

The updated SMOG simulations provided detailed baseline calculations of ambient pollutant levels at CHS locations. A series of SMOG simulations for specific episode conditions were provided to the exposure assessment team, including a detailed quantification of the spatially resolved background abundances for use with the CALINE4 model. Predictions included regional-scale gas and particle distributions and time variations associated with transported and local non-mobile sources corresponding to each of the CHS study areas. The SMOG predictions for different seasons and sub-regions were combined with roadway pollutant profiles from the CALINE4 model to provide the most detailed characterization to date of exposure to roadway pollutants.

UF Near Freeways. New modeling tools were developed and applied to characterize UF near major roadways, including a novel analytical microphysics parameterization that predicts particulate mass and modal size structure as a function of downwind distance from a roadway. Field-measurements near freeways were employed to test and validate the parameterization. The analytical scheme was coupled to the CALINE 4 line source code to achieve high spatial resolution. The emission rates of UFs from major roadways were then estimated using traffic data.

Exposure Assessment

Exposure Assessment for the CHS Children. We developed an Individual Exposure Model (IEM) to retrospectively estimate the long-term average exposure of the individual CHS children to vehicle-related pollutants, including CO, NO2, PM10, PM2.5 and elemental carbon (PM2.5 portion). Children’s time-activity patterns were tracked in five microenvironments where children spend most of their time. A time-activity submodel was developed to create 24-hr time-activity series for each child in the CHS cohort by using information from both the CHS survey and the U.S. Environmental Protection Agency (EPA) Consolidated Human Activity Database (CHAD). The CHS children were grouped by age, gender, day-type, time outdoors and time-in-vehicles. For each CHS category a child was grouped into, the corresponding CHAD distribution was sampled.

The study showed the ratio of pollutant concentrations from transport and local non-mobile sources was correlated inversely with traffic density. Most PM10 and PM2.5 came from transport and local non-mobile source emissions, in agreement with recent studies showing that PM10 and PM2.5 act more like regional pollutants rather than reflecting direct emissions from motor sources.

We found local traffic significantly increased within-community variability for exposure to CO, NO2, and PM-associated pollutants, especially at communities with heavy traffic (e.g. Long Beach). The overall within-community variability of personal exposures (including local traffic effects and time-activity differences) were highest for NO2 (±20–40%), followed by EC (±17–27%), PM10 (± 15–25%), PM2.5 (±15–20%), and CO (±9–14%), where the ranges are across seven CHS communities.

Naphthalene Exposure in the SoCAB. To estimate naphthalene exposure for the SoCAB population naphthalene concentrations predicted by the SMOG model were fed into the Regional Human Exposure (REHEX) model as outdoor pollutant concentrations at a 5-kilometer resolution. Ratios of indoor-to-outdoor (I/O) naphthalene concentrations were obtained from the Fresno Asthmatic Children’s Environment Study, in which 150 naphthalene samples were collected inside and outside 47 non-smoker homes from 2002 to 2003. In the absence of any in-vehicle naphthalene measurements for the SoCAB, an average in-vehicle-to-ambient naphthalene ratio of three was assumed. Time-activity patterns for California residents were obtained from the CHAD.

Results showed mean hourly naphthalene exposures of 270 ng m-3 and 430 ng m-3 for the SoCAB population in the summer and winter episodes, respectively, about 80% higher than the population-weighted outdoor concentrations (150 ng m-3 and 230 ng m-3) because of indoor sources and in-vehicle exposures. More than one million people in the SoCAB were exposed to naphthalene at mean concentrations exceeding 1000 ng m-3 during the winter period, and about 65,000 and 1,300 people, respectively, experienced naphthalene exposures exceeding 2000 ng m-3 and 3000 ng m-3 in the winter case. Population naphthalene exposures correlated strongly with transportation corridors in the SoCAB since gasoline and diesel products and motor vehicle exhaust contribute more than half of the total emissions in the basin. High naphthalene exposures appeared in areas where both emissions and population densities were great, e.g. central Los Angeles.

Improving Spatial Accuracy of Roadway Networks and Geocoded Addresses. Field studies indicate the highest exposures to direct vehicle-related pollutants are highly localized near major roadways suggesting a spatial resolution, down to tens of meters, may be required to better characterize exposure to motor vehicle-related pollutants. The objectives of this study were to develop GIS-based methods to improve the accuracy of roadway network data associated with traffic activities; provide the optimum geocoding data available; and assess the magnitude of potential exposure errors associated with spatially inaccurate roadways and misplaced addresses.

We obtained vehicle activity data for southern California from the California Department of Transportation (Caltrans). The TeleAtlas MultiNet™ USA (TAMN) database was also obtained since it had detailed roadway and address attribute information, a high degree of positional accuracy, and geocoding capability. The Caltrans roadways were based on United States Geological Survey data with traffic activity data, while the TAMN roadways were based on global positioning system (GPS) validation but lacking traffic information. Results showed that in highly urbanized areas there was generally good agreement between the spatial positioning of the Caltrans road network and the TAMN data; however, for some urban areas and several suburban areas, differences on the order of 50 m to 400 m were identified between the two datasets.

For a simple case of light daytime winds (2 m/s, with slightly unstable atmospheric conditions) blowing perpendicular to a busy, at-grade freeway (10,000 vehicles per hour), the CALINE4 model estimated a factor of eight difference in the concentrations of carbon monoxide at receptors located 30 m and 300 m downwind of the roadway centerline. Using a single line to represent a freeway (in Caltrans data) or double lines for two directions of a freeway (in TAMNdata) can also result in different pollutant concentration estimates. The CALINE4 sensitivity test showed that a two-direction freeway scenario resulted in pollutant concentrations 30% lower than a single freeway scenario at a receptor 30 m downwind of the freeway.

This study demonstrated that discrepancies of up to hundreds of meters may exist among different roadway network data, potentially leading to significant misclassification of exposure estimates, up to an order of magnitude in vehicle-exhaust pollutant concentrations. Studies concerned with human exposure to air pollutants adjacent to roadways must account for such discrepancies. We successfully developed and applied a GIS method to address this problem.

Environmental Justice and Traffic-Related Air Pollution in Southern California. The objectives of this research were to identify the geographic pattern of race and poverty in southern California; document the overlap of disadvantaged neighborhoods and the transportation network; and quantify the potential disparities in traffic volume by neighborhood type. Neighborhood measures and traffic volume for block groups were aggregated in five southern California counties by two race-based classifications and four poverty-based classifications. Not surprisingly, we found residents of disadvantaged areas had fewer transportation resources and a lower percentage of workers traveled to work by auto in disadvantaged neighborhoods while a higher percentage traveled by public transportation.

We found road density of high poverty areas was almost two times that of the least poor neighborhoods and minority areas had almost 2.5 times the traffic density of non-minority areas. Very poor areas, which represent the most disadvantaged areas in the region, had a significantly higher traffic density than minority or poor areas, perhaps because these areas have the highest roadway density. Given the magnitude of the disparities in the distribution of traffic by these neighborhoods, there is reason to suspect that residents of minority and poor areas are at a higher risk of the health effects associated with vehicle-related pollutants.

Conclusions:

A new air quality and exposure modeling system was developed that links a regional air quality model (SMOG) with a local line source model (CALINE4), and uses the output to drive an IEM and a REHEX. Thus, detailed statistics on exposure to vehicle-related pollutants can be calculated while accounting for a variety of critical microenvironments, time-activity patterns, and ambient pollutant concentrations at different spatial resolutions. The interdisciplinary work reported here has provided unique information in support of several important health-related projects, including the intra-community exposure variability analyses in the CHS study, assessment of population exposure to naphthalene, and investigation of uncertainties in factors important in epidemiological studies of vehicle-related pollutants such as accuracy of roadway alignments and geocoded addresses.

Technical Report:

Full Final Technical Report (PDF, 26pp., 586KB, about PDF)


Journal Articles on this Report : 6 Displayed | Download in RIS Format

Other subproject views: All 6 publications 6 publications in selected types All 6 journal articles
Other center views: All 150 publications 149 publications in selected types All 149 journal articles
Type Citation Sub Project Document Sources
Journal Article Fruin SA, St Denis MJ, Winer AM, Colome SD, Lurmann FW. Reductions in human benzene exposure in the California South Coast Air Basin. Atmospheric Environment 2001;35(6):1069-1077. R827352 (2004)
R827352 (Final)
R827352C015 (Final)
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  • Journal Article Houston D, Wu J, Ong P, Winer A. Structural disparities of urban traffic in Southern California: implications for vehicle-related air pollution exposure in minority and high-poverty neighborhoods. Journal of Urban Affairs 2004;26(5):565-592. R827352 (2004)
    R827352 (Final)
    R827352C015 (Final)
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  • Abstract: Wiley-Abstract
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  • Journal Article Houston D, Ong P, Wu J, Winer A. Proximity of licensed child care facilities to near-roadway vehicle pollution. American Journal of Public Health 2006;96(9):1611-1617. R827352 (Final)
    R827352C015 (Final)
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  • Journal Article Lu R, Wu J, Turco RP, Winer AM, Atkinson R, Arey J, Paulson SE, Lurmann FW, Miguel AH, Eiguren-Fernandez A. Naphthalene distributions and human exposure in Southern California. Atmospheric Environment 2005;39(3):489-507. R827352 (2004)
    R827352 (Final)
    R827352C013 (Final)
    R827352C015 (Final)
    R831861 (2004)
    R831861 (2005)
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  • Journal Article Wu J, Lurmann F, Winer A, Lu R, Turco R, Funk T. Development of an individual exposure model for application to the Southern California Children's Health Study. Atmospheric Environment 2005;39(2):259-273. R827352 (Final)
    R827352C015 (Final)
    R828172 (Final)
    R831845 (2005)
    R831861 (2004)
    R831861 (2005)
    R831861 (Final)
    R831861C001 (Final)
    R831861C002 (Final)
    R831861C003 (Final)
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  • Journal Article Wu J, Funk T, Lurmann F, Winer A. Improving spatial accuracy of roadway networks and geocoded addresses. Transactions in GIS 2005;9(4):585-601. R827352 (Final)
    R827352C015 (Final)
    R831845 (2005)
    R831861 (2005)
    R831861 (Final)
    R831861C001 (Final)
    R831861C002 (Final)
    R831861C003 (Final)
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  • Supplemental Keywords:

    RFA, Health, Scientific Discipline, Air, HUMAN HEALTH, particulate matter, Environmental Chemistry, Air Pollutants, Risk Assessments, Biochemistry, Health Effects, Atmospheric Sciences, ambient aerosol, asthma, particulates, morphometric analyses, human health effects, toxicology, airway disease, ambient measurement methods, air pollution, PAH, human exposure, toxicity, particulate exposure, aerosol composition, allergens, aerosols, atmospheric chemistry, human health risk, particle transport, particle concentrator, particle size measurement

    Relevant Websites:

    Full Final Technical Report (PDF, 26pp., 586KB, about PDF)
    http://www.scpcs.ucla.edu Exit

    Progress and Final Reports:

    Original Abstract
  • 1999
  • 2000
  • 2001 Progress Report
  • 2002 Progress Report
  • 2003 Progress Report
  • 2004 Progress Report

  • Main Center Abstract and Reports:

    R827352    Southern California Particle Center and Supersite

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827352C001 The Chemical Toxicology of Particulate Matter
    R827352C002 Pro-inflammatory and the Pro-oxidative Effects of Diesel Exhaust Particulate in Vivo and in Vitro
    R827352C003 Measurement of the “Effective” Surface Area of Ultrafine and Accumulation Mode PM (Pilot Project)
    R827352C004 Effect of Exposure to Freeways with Heavy Diesel Traffic and Gasoline Traffic on Asthma Mouse Model
    R827352C005 Effects of Exposure to Fine and Ultrafine Concentrated Ambient Particles near a Heavily Trafficked Freeway in Geriatric Rats (Pilot Project)
    R827352C006 Relationship Between Ultrafine Particle Size Distribution and Distance From Highways
    R827352C007 Exposure to Vehicular Pollutants and Respiratory Health
    R827352C008 Traffic Density and Human Reproductive Health
    R827352C009 The Role of Quinones, Aldehydes, Polycyclic Aromatic Hydrocarbons, and other Atmospheric Transformation Products on Chronic Health Effects in Children
    R827352C010 Novel Method for Measurement of Acrolein in Aerosols
    R827352C011 Off-Line Sampling of Exhaled Nitric Oxide in Respiratory Health Surveys
    R827352C012 Controlled Human Exposure Studies with Concentrated PM
    R827352C013 Particle Size Distributions of Polycyclic Aromatic Hydrocarbons in the LAB
    R827352C014 Physical and Chemical Characteristics of PM in the LAB (Source Receptor Study)
    R827352C015 Exposure Assessment and Airshed Modeling Applications in Support of SCPC and CHS Projects
    R827352C016 Particle Dosimetry
    R827352C017 Conduct Research and Monitoring That Contributes to a Better Understanding of the Measurement, Sources, Size Distribution, Chemical Composition, Physical State, Spatial and Temporal Variability, and Health Effects of Suspended PM in the Los Angeles Basin (LAB)