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Ambient Particulate Matter Exposures: A Comparison of Sheds-PM Exposure Model Predictions and Estimates Derived from Measurements Collected During Nerl's RTP PM Panel Study
Citation:
Burke, J M., A W. Rea, J C. Suggs, R W. Williams, J Xue, AND A H. Ozkaynak. Ambient Particulate Matter Exposures: A Comparison of Sheds-PM Exposure Model Predictions and Estimates Derived from Measurements Collected During Nerl's RTP PM Panel Study. Presented at International Society of Exposure Analysis 2002 Conference, Vancouver, Canada, August 11-15, 2002.
Impact/Purpose:
The primary objective of this research is to improve current PM population exposure models to more accurately predict exposures for the general population and susceptible sub-populations. Through model improvements, a better understanding of the major factors controlling exposure to PM will be achieved. Specific objectives of this research are to:
- predict total personal exposure to PM10 and PM2.5 for the general and for susceptible sub-populations residing in different urban environments
- estimate the contribution of ambient PM to predicted total PM exposures
- determine what factors are of primary importance in determining PM exposures, including an analysis of the effects of time spent in various microenvironments and the importance of spatial variability in ambient PM concentrations
- determine what factors contribute the greatest uncertainty to model predictions and make recommendations for measurement and modeling studies to reduce these uncertainties
- predict daily and annual average exposures using single or multi-day time-activity diaries
- incorporate state-of-the-art dosimetric models of the lung into PM population exposure and dose models
- evaluate models against measured data from PM panel and other exposure measurement studies
- develop exposure and dose metrics applicable to acute and chronic environmental epidemiology studies
Description:
The US EPA National Exposure Research Laboratory (NERL) is currently refining and evaluating a population exposure model for particulate matter (PM), called the Stochastic Human Exposure and Dose Simulation (SHEDS-PM) model. The SHEDS-PM model estimates the population distribution of PM exposures by randomly sampling from distributions of ambient PM concentrations and exposure factors to estimate the distribution of PM exposures in various microenvironments (e.g., indoors at home, in vehicles, outdoors, etc.). SHEDS-PM model output also includes estimated contributions of these microenvironments to predicted total PM exposure, as well as the contribution from both PM of ambient origin and indoor sources of PM in these microenvironments.
An application of the SHEDS-PM model was implemented using measurement data from the NERL RTP PM Panel Study. The study included daily measurements of PM2.5 personal exposure, as well as indoor residential, outdoor residential and ambient (central site) PM2.5 concentrations, during a 7-day study period for each participant within each of the four seasons from June 2000 - May 2001. Daily measurements of ambient PM2.5 concentrations and residential air exchange rates, and human activity pattern data obtained from daily diaries for each participant were used as input to the model. Additional model inputs, such as demographic data and residential characteristics, were matched to the RTP PM Panel Study population.
The distribution of daily average total PM2.5 exposures predicted by the SHEDS-PM model compared well with the measurements of personal PM2.5 exposures from the RTP PM Panel Study. The median total PM2.5 exposure (50th percentile) for the SHEDS-PM predictions was 21 ug/m3 compared to 19 ug/m3 for the personal PM2.5 exposure measurements. The median personal exposure to ambient PM2.5 predicted by the model was 9 ug/m3 for the study population and ranged from 2 - 38 ug/m3. Predicted ambient PM2.5 exposures were not a consistent fraction of the ambient central site PM2.5 concentrations for the simulated population. The median ratio of the predicted ambient PM2.5 exposure to ambient PM2.5 concentration was 0.6, with 95% of the simulated population having ratios between 0.3 and 0.8. The model results were compared to estimates of ambient PM2.5 exposures derived from analysis of 24-hr integrated and continuous personal PM2.5 measurement data collected during the study. This comparison was used to evaluate the SHEDS-PM model prediction of population exposures to ambient PM2.5 and indicated that the model results were generally consistent with the estimates derived from measurement data.
This work has been funded wholly by the United States Environmental Protection Agency under contract #68-D-99-012 to the Research Triangle Institute and assistance agreement #CR-828186-01-0 to Shaw University. It has been subjected to Agency review and approved for publication.