2004 Progress Report: Modeling Relationships Between Mobile Source Particle Emissions and Population Exposures

EPA Grant Number: R827353C012
Subproject: this is subproject number 012 , established and managed by the Center Director under grant R827353
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Mickey Leland National Urban Air Toxics Research Center (NUATRC)
Center Director: Beskid, Craig
Title: Modeling Relationships Between Mobile Source Particle Emissions and Population Exposures
Investigators: Koutrakis, Petros
Current Investigators: Spengler, John D. , Evans, John S. , Greco, Susan L , Levy, Jonathan , Stevens, G. , Wilson, A.
Institution: Harvard University
Current Institution: Harvard T.H. Chan School of Public Health , Harvard University
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, 2003 through May 31, 2004
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


For year 6 of the project, we had proposed extending our intake fraction (iF) methodology to address motor vehicle emissions, as a way of informing PM control decisions and future analyses.  Our specific objectives were to:

  • Evaluate geographic patterns in primary and secondary particulate matter iFs for mobile sources, using a national-scale source-receptor (S-R) matrix
  • Determine the relative contributions of near-source and long-range populations to particulate matter iFs for mobile sources in different geographic locations
  • Develop predictive regression equations for iFs to explain geographic patterns as a function of population density and meteorological covariates.

Progress Summary:

We have completed this analysis, with the following key findings:

  • For primary fine particulate matter emitted from mobile sources, the intake fractions varied across source counties from 0.14 to 23 per million (median of 1.2 per million). These values were highly correlated with near-source population density; the population in the source county explained 43 percent of the variability in the above estimates, and a multivariate regression model with population at various radii from the source explained 86 percent of the variability. Spatial analyses of residuals indicated generally strong model performance, with greater errors along the coasts, where wind fields are more difficult to characterize and downwind populations may be less significant.
  • For secondary ammonium sulfate formed from SO2 emissions, the median intake fraction (0.43 per million) was somewhat lower than for primary PM. The variability was similar to that for primary PM, but with more regional variability rather than small-scale spatial variability. In spite of the regional influence on atmospheric chemistry, multivariate regressions with only population terms had an R2 of 0.78, indicating the significance of population patterns even in this context. However, there was relatively greater statistical significance for population beyond 200 km from the source, relative to primary PM, and relatively lower statistical significance for population within 200 km, reflecting expected concentration patterns.
  • Secondary ammonium nitrate formed from NOx emissions had an even lower median intake fraction (0.072 per million), with spatial variability driven somewhat by population patterns (R2 of 0.63 in multivariate regression model) but also by relative ambient concentrations of sulfate, nitrate, and ammonium. Higher values tended to be found in the Midwest, where there is adequate ammonia to neutralize nitrate (and lower ambient sulfate), versus higher levels in the Ohio River Valley and Northeast for secondary sulfate and primary PM.
  • We also quantified the extent to which SO2 controls might free up ammonia to react with nitrate, thereby increasing ammonium nitrate concentrations. We determined that the public health benefits of SO2 emission controls (due to sulfate reductions) would be offset by ammonium nitrate increases by an average of 9 percent, ranging from 1 percent to 29 percent across U.S. counties.
  • As mentioned above, one of our primary objectives was to determine the relative importance of near-source and long-range populations. The median distances within which half of the total intake fraction was realized was about 150 km for primary PM, 450 km for secondary sulfate, and 390 km for secondary nitrate. However, these values varied substantially by setting (i.e., range for primary PM from 0 km, indicating that more than 50 percent of the iF was realized in the source county, to 1800 km). In dense urban areas, often a majority of the intake fraction was realized within the source county, indicating that more geographically resolved dispersion modeling may be warranted.

Comparing our results with the published literature to date, the magnitude of our estimates appear reasonable, and this analysis remains the first attempt to characterize spatial variability in mobile source intake fractions and to derive conclusions about the model scope and resolution needed to accurately estimate public health benefits of pollution control from mobile sources. Specifically, we concluded that a national-scale county-resolution dispersion model is likely sufficient for secondary particulate matter or primary particulate matter in rural areas with substantial downwind populations, but that more resolved models should be explored in dense urban areas or less-populated areas without significant downwind populations.

The manuscript based on this work is undergoing final revisions and will be submitted to the journal Atmospheric Environment in September 2005. It will be submitted jointly with a power plant intake fraction analysis derived from Wilson (2003), a manuscript also supported by the EPA Particle Center at HSPH.

Based on the findings from this analysis, we have proceeded with follow-up work addressing potential within-county heterogeneity in primary PM mobile source intake fractions, as well as the questions of the spatial extent of the iF for sources within urban areas and the potential biases in estimates based on county-level resolution. We are using the CALINE dispersion model to simulate the influence of line-source emissions on concentrations under a variety of meteorological conditions, population patterns, and building/road configurations (i.e., presence/absence of a street canyon). This simulation will allow us to determine heterogeneity in primary PM intake fractions as well as the circumstances under which the near-source populations may dominate the intake fraction. Model development is ongoing and initial findings will be presented at the International Society for Exposure Analysis conference in November 2005.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this subproject

Supplemental Keywords:

exposure, health effects, susceptibility, metals, public policy, biology, engineering, epidemiology, toxicology, environmental chemistry, monitoring, air pollutants, air pollution, air quality, ambient air, ambient air monitoring, ambient air quality, ambient measurement methods, ambient monitoring, ambient particle health effects, ambient particles, animal inhalation study, assessment of exposure, biological mechanism, biological response, cardiopulmonary, cardiopulmonary response, cardiovascular disease, chemical exposure, children, developmental effects, dosimetry, environmental health hazard, exposure and effects, genetic susceptibility, health risks, human exposure, human health, human health effects, human health risk, human susceptibility, indoor air quality, indoor exposure, inhalation, inhalation toxicology, inhaled particles, lead, measurement methods, particle exposure, particulate exposure, particulates, pulmonary, pulmonary disease, respiratory, respiratory disease, risk assessment, sensitive populations, stratospheric ozone,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, ENVIRONMENTAL MANAGEMENT, HUMAN HEALTH, Air Pollution Monitoring, particulate matter, Toxicology, air toxics, Environmental Chemistry, Epidemiology, Air Pollution Effects, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, Environmental Monitoring, Health Effects, Physical Processes, Children's Health, genetic susceptability, indoor air, tropospheric ozone, Molecular Biology/Genetics, Biology, Environmental Engineering, Risk Assessment, ambient air quality, interindividual variability, microbiology, molecular epidemiology, monitoring, particulates, sensitive populations, chemical exposure, air pollutants, cardiopulmonary responses, health risks, human health effects, indoor exposure, ambient air monitoring, exposure and effects, ambient air, ambient measurement methods, exposure, lead, pulmonary disease, developmental effects, epidemelogy, biological response, respiratory disease, air pollution, ambient monitoring, children, Human Health Risk Assessment, particle exposure, biological mechanism , cardiopulmonary response, human exposure, inhalation, mobile sources, pulmonary, susceptibility, particulate exposure, assessment of exposure, ambient particle health effects, PM, epidemeology, human susceptibility, environmental health hazard, inhalation toxicology, cardiopulmonary, indoor air quality, inhaled particles, modeling studies, measurement methods , air quality, cardiovascular disease, dosimetry, human health risk, metals, respiratory, genetic susceptibility

Progress and Final Reports:

Original Abstract
  • 1999
  • 2000
  • 2001
  • 2002
  • 2003
  • Final Report

  • Main Center Abstract and Reports:

    R827353    Mickey Leland National Urban Air Toxics Research Center (NUATRC)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827353C001 Assessing Human Exposures to Particulate and Gaseous Air Pollutants
    R827353C002 Quantifying Exposure Error and its Effect on Epidemiological Studies
    R827353C003 St. Louis Bus, Steubenville and Atlanta Studies
    R827353C004 Examining Conditions That Predispose Towards Acute Adverse Effects of Particulate Exposures
    R827353C005 Assessing Life-Shortening Associated with Exposure to Particulate Matter
    R827353C006 Investigating Chronic Effects of Exposure to Particulate Matter
    R827353C007 Determining the Effects of Particle Characteristics on Respiratory Health of Children
    R827353C008 Differentiating the Roles of Particle Size, Particle Composition, and Gaseous Co-Pollutants on Cardiac Ischemia
    R827353C009 Assessing Deposition of Ambient Particles in the Lung
    R827353C010 Relating Changes in Blood Viscosity, Other Clotting Parameters, Heart Rate, and Heart Rate Variability to Particulate and Criteria Gas Exposures
    R827353C011 Studies of Oxidant Mechanisms
    R827353C012 Modeling Relationships Between Mobile Source Particle Emissions and Population Exposures
    R827353C013 Toxicological Evaluation of Realistic Emissions of Source Aerosols (TERESA) Study
    R827353C014 Identifying the Physical and Chemical Properties of Particulate Matter Responsible for the Observed Adverse Health Effects
    R827353C015 Research Coordination Core
    R827353C016 Analytical and Facilities Core
    R827353C017 Technology Development and Transfer Core