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 220 Significant Research Findings: A Probabilistic Exposure Model Capable of Estimating Population Exposures to PM Components Scientific EPA's National Ambient Air Quality Standards (NAAQS) for particulate matter Problem and (PM) are largely based on studies that have shown consistent associations between Policy Issues increases in PM concentrations measured at outdoor sites within a community and the occurrence of adverse health effects in the population living there. However, the PM concentrations measured in outdoor air may not be the same as in the air people breathe during their daily activities, for example while indoors at home, work, or school, or when traveling in vehicles. Understanding actual personal exposures to PM provides an important link between PM regulatory monitoring and the risk of adverse health effects. The National Research Council (NRC) lists understanding PM exposures as one of the ten highest priority research areas for PM. (Cf. Research Priorities for Airborne Particulate Matter: IV. Continuing Research Progress National Academies Press, 2004.) The first two NRC Research Topics focus on understanding exposures of susceptible subpopulations, such as the elderly and children, to PM mass concentrations and how these exposures relate to concentrations measured at outdoor community sites. The second Research Topic extends the exposure research to the potentially toxic components of PM, such as sulfate, nitrate, various metals, and organic and elemental carbon, as well as to the different PM size fractions, including the ultra-fine fraction. To address these research areas identified by the NRC, new data and models are needed that can estimate individual, subpopulation, and general population exposures to PM (and its biologically important constituents) and to relate those exposures to PM concentrations measured at outdoor sites. Research EPA's National Exposure Research Laboratory (NERL) has developed a model to Approach estimate distribution of PM exposures (amount available in the air for an individual to breathe) and intake dose (amount inhaled into the lungs) for the general population or for a targeted sub-population. U.S. census data built into the model 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 algorithms that depend on the outdoor PM concentration, but also ------- account for indoor PM sources. Each individual's exposure profile is then calculated from the time spent in each location 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 intake-dose distributions from both outdoor and indoor sources of PM. Results and The result of this research is Version 2.0 of the Stochastic Human Exposure and Impact Dose Simulation (SHEDS) model for PM. The EPA SHEDS-PM 2.0 model estimates the range in PM exposure and/or intake-dose across a population of interest, and percentage of estimated exposures above a certain level. The model includes a user-friendly interface that allows the user to define the model run scenario and input data, as well as to analyze and display the results. The availability of data on PM constituents needed as input to the SHEDS-PM 2.0 model can vary significantly between the different PM species. The model is structured to allow the user to provide the required inputs based on the level of information available for that particular PM component. For example, the user has different options for specifying the relationship between the outdoor air concentrations of a PM component and the concentrations in locations where people spend their time. The model results can be used to assess potential exposures to PM components for a community of interest, to estimate the impact of different air concentration patterns resulting from possible emissions reduction strategies on population exposures, and to improve exposure characterization in epidemiology studies. Collaboration with EPA/NERL on this research effort included contributions from Science Applications International Corporation (SAIC). Examples of recent publications from this study include the following: Burke, J., Zufall, M., 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 (2001) 11, 470-489. Burke, J., Vedantham, R., McCurdy, T., Xue, J., 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. Burke, J.M., Vedantham, R., McCurdy, T., Xue, J., 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. Future Research Recent human exposure measurement studies have produced data on PM components from residential indoor, outdoor, and personal exposure samples. As more of the data from these studies become available, EPA/NERL will use the data to refine the SHEDS-PM 2.0 model inputs and to evaluate model predictions. A longer term goal is to use observational data and SHEDS exposure model predictions to describe and understand human exposures to particulates derived from various source types, since recent findings show a variety of health effects Research Collaboration and Research Products ------- associated with PM from specific sources. EPA/NERL will combine source apportionment techniques with exposure models to evaluate the ambient-personal exposure relationship for PM from various sources. EPA/NERL will also investigate the influence of the spatial distribution of sources on exposure. Contacts for Questions and inquiries can be directed to the principal investigator: Additional T ~ ^ 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 No. 69W99002 and 68W00122 to Science Applications International Corporation (SAIC). ------- |