United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory Research Abstract Government Performance Results Act (GPRA) Goal 1 Annual Performance Measure 19 Significant Research Findings: Probabilistic Exposure and Dose Model for Estimating Population Exposures to Particulate Matter Scientific In July 1997, the EPA Administrator issued new National Ambient Air Quality Problem and Standards (NAAQS) for particulate matter (PM). The new standards were largely Policy Issues based on epidemiological studies that found consistent associations between PM concentrations measured at central site monitors and various adverse health effects. However, individuals may develop an adverse health response to PM in the air they breathe, not the air from a central site monitor. Thus, understanding personal exposures to ambient PM provides a critical link between regulatory monitoring and health outcomes. Specifically, understanding the relationship between PM concentrations measured at central site monitors and residential outdoor, indoor, and personal exposure concentrations of PM is essential to understanding risks. In the same year the NAAQS PM standards were revised, the National Research Council (NRC) identified 10 priority research areas that would reduce "uncertainties in the scientific evidence used to guide regulation of airborne particulate matter in the United States." Two of the 10 highest-priority research activities were directed toward understanding PM exposures. Research Topic 1 focused on understanding how susceptible subpopulations are exposed to ambient PM mass and how these exposures relate to concentrations at a central monitor. Research Topic 2 extended the research to address potentially toxic components of PM and the general population as well as susceptible subpopulations. To address these NRC research areas, data and models are needed to predict human exposure to PM based on measurements made at central sites. Research EPA's National Exposure Research Laboratory (NERL) developed a model to Approach estimate the population distribution of PM exposure (amount available for contact with an individual) and dose (amount inhaled or deposited in the lungs) to better understand the relationship between personal exposures and community central site measurements of PM. U.S. census data are used to create the simulated population. Human activity pattern data, also built into the model, are assigned to each simulated individual to account for the way people interact with their environment. The user is only required to provide ambient PM concentration data, which can be monitoring data or output from an air quality dispersion model. PM concentrations in the indoor locations where people spend much of their time ------- (such as home, work, or school) are calculated using equations that depend on the outdoor PM concentration and also account for indoor PM sources. Each individual's exposure profile is then calculated from the time spent in each location (indoors, outdoors, in a vehicle) and the PM concentration in that location. Activity-specific inhalation rates while in each location are also calculated by the model and combined with the exposure concentrations to estimate an intake-dose profile for each individual. Daily-averaged values are calculated from the daily exposure and dose profiles and then combined to provide distributions for the user-defined population. Statistical methods are used to incorporate variability and uncertainty into the model input parameters. Model output includes estimates of the contribution to exposure and dose distributions from both outdoor and indoor sources of PM. Results and The main product of this research is the Stochastic HumanExposure and Dose Impact Simulation (SHEDS) model for particulate matter (PM). The SHEDS-PM model estimates the range in PM exposure and/or dose across a population of interest and the likelihood of exposures above a certain level. The model includes a user- friendly interface that allows for user specification of the model run scenario and input data, as well as for analysis and display of results. EPA's Office of Air and Radiation, Regional Offices, and State agencies can use the SHEDS-PM model to estimate population exposures to PM using PM monitoring data or dispersion model output. The model also provides estimates of population exposures to PM of outdoor origin separately from exposures to indoor sources of PM, information critical for understanding personal exposures to PM but unavailable through monitoring approaches. This information can be used to improved exposure characterization in epidemiology studies. Collaboration with EPA/NERL on this research effort included contributions from the Environmental and Occupational Health Sciences Institute (EOHSI) and from Science Applications International Corporation (SAIC). Examples of recent publications from this study include: Burke, J., Zufall, M., and Ozkaynak, H. "A Population exposure model for particulate matter: Case study results for PM2.5 in Philadelphia, PA." Journal of Exposure Analysis and Environmental Epidemiology 11: 470 - 489, 2001. Burke, J.M., Vedantham, R., McCurdy, T., Xue, J., and Ozkaynak, H. "SHEDS-PM: A population exposure model for predicting distributions of PM exposure and dose from both outdoor and indoor PM sources." Presented at the 13th annual conference of the International Society of Exposure Analysis, Stresa, Italy. September, 2003. Burke, J., Vedantham, R., McCurdy, T., Xue, J., and Ozkaynak, H. "A Population Exposure Model for Particulate Matter: SHEDS-PM." Presented at the 21st annual conference of the American Association of Aerosol Research (AAAR), Charlotte, NC. October, 2002. Georgopoulos, P., Wang, S., Vyas, V., Sun, Q., Burke, J., Vedantham, R., McCurdy, T., and Ozkaynak, H. "A Source-to-Dose Assessment of Population Exposures to Fine PM and Ozone in Philadelphia, PA, during a Summer 1999 Episode." Journal of Exposure Analysis and Environmental Epidemiology (submitted), 2003. Research Collaboration and Research Products ------- Future Research The SHEDS-PM model will be modified and enhanced to estimate population exposure and dose for various components of particulate matter that are associated with health effects, as directed by NRC Research Topic 2. These toxic PM components include chemical species such as sulfate, nitrate, metals, and elemental/organic carbon, as well as additional size fractions such as ultrafine PM. Research activities will focus on enhancing the model and developing new model inputs and algorithms for case study applications. In light of recent findings showing health effects associated with PM from specific sources, source apportionment techniques will be incorporated into exposure models in order to evaluate the ambient-personal exposure relationship for PM from various sources. The influence of spatial distribution of sources on exposure will also be investigated. Contacts for Questions and inquiries can be directed to the principal investigator: Additional Information Janet M Burke Ph D U.S. EPA, Office of Research and Development National Exposure Research Laboratory Mail Drop E205-02 109 T.W. Alexander Drive Research Triangle Park, NC 27711 Phone: 919/541-0820 E-mail: burke.janet@epa.gov Federal funding for this research was administered under EPA Contract #69W99002 to Science Applications International Corporation (SAIC), and EPA Cooperative Agreement #CR827033 to Environmental and Occupational Health Sciences Institute (EOHSI). ------- |