2003 Progress 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: Winer, Arthur M. , Turco, Richard , Lurmann, Fred
Current 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)
Project Period Covered by this Report: June 1, 2002 through May 31, 2003
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


The overall objective of this research project is to utilize the University of California at Los Angeles’ Regional Human Exposure (REHEX) model and Surface Meteorology and Ozone Generation (SMOG) airshed models to develop more precise and comprehensive human exposure models that: (1) provide an accurate and comprehensive assessment of exposure to particulate matter (PM) and other vehicle-related pollutants in Southern California populations; (2) enhance health effects investigations underway in the Southern California Particle Center and Supersite (SCPCS) and Children’s Health Study (CHS); and (3) create linkages between emission sources, exposures, and health endpoints.

This is one of the project progress reports for the SCPCS. The progress for the other research projects conducted by the Center is reported separately (see reports for R827352, R827352C001 through R827352C004, and R827352C006 through R827352C021).

Progress Summary:

Progress on Airshed Modeling

Progress made included the assessment of the regional distributions of, and human exposure to, naphthalene and naphthoquinones in the Los Angeles Basin, application of the SMOG model in support of the SCPCS and CHS, and initial development of a detailed model for ultrafine particle size distributions for freeway exposure studies.

Exposure to naphthalene and naphthoquinones may have significant adverse health effects. We investigated the regional distributions of naphthalene and its byproducts over Southern California. We found that gasoline and diesel engine exhaust, with related fuel vaporization, contribute roughly half of the daily total naphthalene burden in Southern California. The spatial distribution patterns of emissions are highly correlated with major roadways in the region owing to the importance of vehicular exhaust as a naphthalene source. We verified the emission inventory for naphthalene against new field measurements undertaken by the SCPCS (Miguel, et al.) at the Sepulveda tunnel near the Los Angeles International Airport and in ambient air samples collected at the California Institute of Technology at Pasadena. The agreement between modeled and measured naphthalene-to-benzene ratios indicates the relative contributions to the total naphthalene emissions from mobile sources are represented reasonably well in our emission inventory.

The SMOG airshed model was used to compute the spatial and temporal distributions of naphthalene and its photooxidation products throughout the region. Our simulations are unique, offering for the first time a comprehensive and unified picture of airborne naphthalene for health impact assessment. The SMOG simulations reveal definite patterns in naphthalene distribution and exposure, with large spatial variations. The results also show large diurnal and seasonal variations to a much greater degree than can be inferred from existing measurements. Peak naphthalene concentrations are estimated to occur in the early morning hours in the winter.

To improve our predictions of particulate pollutant distributions for exposure assessment in the South Coast Air Basin (SoCAB), we updated the primary emission inventories, incorporated a secondary organic aerosol module, and integrated a biogenic emission database into the SMOG model. The latest emission inventory developed for the South Coast Air Quality Management District 2003 Air Quality Management Plan was adopted to estimate CO, NOx, SOx, volatile organic compound, and PM emissions in the SoCAB. The enhancements to the SMOG model have significantly improved our ability to model the distributions and organic composition of particulates and their precursors in the SoCAB. The updated emission inventories also allow more reliable simulations of criteria pollutants of interest in exposure assessments for the individual children in the CHS.

We set up a high-resolution two-dimensional version of the SMOG model that includes explicit treatments of aerosol microphysics and chemistry in the configuration of a line emission source. This model, which requires more development in Year 6 of the project, will provide a comprehensive basis for investigating local exposure to ultrafine particles.

Progress on Exposure Modeling

In Year 5 of the project, significant progress has been made in improving individual and population exposure assessments for vehicle-related pollutants in the SoCAB. We investigated spatial accuracy issues in roadway data and geocoding processes to provide the most accurate data for exposure and epidemiological studies concerned with vehicle-related air pollution. Large discrepancies, up to hundreds of meters, were found between a widely used U.S. Geological Survey (USGS) roadway network containing traffic activity data and a global positioning system (GPS)-validated road network without traffic information, with the GPS-validated network having higher spatial accuracy. We demonstrated that discrepancies in roadway geometry of this magnitude, as well as geocoding errors, can lead to serious exposure misclassifications on the order of factors of 3 to 10 in assigned pollutant concentrations. The geographic information system-based algorithm we developed was effective in transferring vehicle activity information from the less accurate USGS roadway network to a GPS-accurate road network, with a match rate exceeding 95 percent. This method is portable and can be employed to transfer vehicle activity and other data between roadway networks.

By linking the SMOG and REHEX models, we quantified the population exposure to naphthalene for the first time for the California SoCAB. Average hourly naphthalene exposures in the SoCAB under summer and winter conditions were 270 ng m-3 and 430 ng m-3, respectively. More than 1 million and 1,000 individuals were estimated to experience naphthalene exposure greater than 1,000 and 3,000 ng m-3, respectively. Substantial spatial and temporal variations exist for naphthalene exposures, with populations living, working, or attending school adjacent to major roadways experiencing the highest exposures. Indoor sources and travel by vehicles accounted for 40 percent and 4 percent of the total exposure, respectively, whereas environmental tobacco smoke accounted for less than 5 percent of total naphthalene exposures. The highest naphthalene exposures estimated from this modeling study exceed the reference concentration for chronic inhalation exposure adapted by the U.S. Environmental Protection Agency.

Environmental inequities in Southern California also were investigated with respect to disproportionate exposure to vehicle-generated pollutants. Minority and high-poverty neighborhoods were found to have a higher population density, lower levels of educational attainment, higher rates of unemployment, lower housing value, older and more multifamily housing, higher density of highways and major roads, and fewer transportation resources. We determined that these neighborhoods bear more than two times the level of traffic density compared to the rest of the Southern California region, which may associate them with a higher risk of exposure to vehicle-related pollutants both directly and because of penetration of outdoor air into older, more poorly constructed housing with higher than average air exchange rates.

Future Activities:

The specific objectives of the SCPCS modeling program during Year 6 of the project are to:

  • Simulate the dispersion and aging of ultrafine particles downwind of major roadways under field conditions and model both individual and regional exposure to ultrafine particles using appropriate exposure models.
  • Calculate the regional distributions of organic particulate and elemental carbon with the SMOG model and the resulting regional population exposures using the REHEX model.
  • Correlate the emission sources of key species with specific human receptor exposures.
  • Further improve assessments of in-vehicle exposures to ultrafine particles and other vehicle-related pollutants for the SoCAB population and individuals (e.g., CHS children).
  • Investigate the relationship between ethnicity and socioeconomic status and spatially resolved population exposures to vehicle-related pollutants.

Journal Articles:

No journal articles submitted with this report: View all 6 publications for this subproject

Supplemental Keywords:

particulate matter, PM, quinones, polycyclic aromatic hydrocarbons, PAHs, aldehydes, ketones, metals, human exposure studies, atmospheric aerosol, environmental monitoring, modeling, airshed model, human exposure model, California, CA, acute exposure, aerosols, air pollution, air quality, air toxics, ambient aerosol, assessment of exposure, atmospheric chemistry, bioaerosols, childhood respiratory disease, children, Children’s Health Study, dosimetry, environmental hazard exposures, environmental health hazard, exposure assessment, health effects, human exposure, human health effects, inhaled particles, lead, outdoor air, particle concentrator, particle transport, particulate exposure, particulates, sensitive populations, toxicology, toxics,, 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:

http://www.scpcs.ucla.edu/exit EPA

Progress and Final Reports:

Original Abstract
  • 1999
  • 2000
  • 2001 Progress Report
  • 2002 Progress Report
  • 2004 Progress Report
  • Final 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)