Quantification and Source Apportionment of Human Exposure to Atmospheric Fine Particulate Matter

PM2.5 exposure is associated with short-term and chronic respiratory effects. Therefore, there is a need to investigate human exposure to PM2.5 in order to support assessment of the association between exposure and adverse health effects. The methodology used in the current version of Stochastic Exposure and Dose Simulation Model for Particulate Matter (SHEDS-PM) for in-vehicle PM2.5 concentration is reviewed. An alternative approach of estimating in-vehicle PM2.5 concentration based on the use of a dispersion model to estimate near-road PM2.5 concentration and a mass balance model for estimating in-vehicle concentration has been specified and applied. In-vehicle concentration is estimated based on air exchange rate and filter efficiency. In-vehicle concentration varies with road type, traffic flow, wind speed, stability class, and ventilation. Average in-vehicle exposure is estimated to contribute 10 to 20 percent of average daily exposure. The contribution of in-vehicle exposure to total daily exposure can be higher for some individuals. Recommendations are made for updating exposure models and implementation of the alternative approach.;To relate adverse health effects to PM2.5 sources and to develop effective control strategy for PM2.5, source apportionment studies for exposure of PM2.5 are needed to determine the contributions of PM2.5 sources to exposure. The objectives are to: (a) identify geographic and seasonal variability in source contributions to total PM 2.5 exposure; and (b) analyze factors that cause the variability. The Stochastic Human Exposure and Dose Simulation Model for PM2.5 (SHEDS-PM) was used to apportion non-ambient PM sources and to determine contribution of ambient exposure to total exposure. U.S. EPA Speciation Trends Network (STN) speciated PM2.5 fixed site monitoring data for 10 sites in three geographic areas (Texas, North Carolina, and New York City) were used to characterize the composition of ambient PM2.5 over space and the study periods are April, July, October and December 2002. Secondary sulfate and motor vehicles are found to contribute most to total exposure among all ambient sources for all sites. Home smoking contributes most to total exposure for smokers and non-smokers living with smokers. Home cooking contributes most to total exposure for non-smokers not living with smokers among non-ambient sources. Seasonal and geographical variability of source apportionment are strongly affected by air exchange rates. Exposure apportionment for two age groups, people 12 years old and under, 65 years old and under are also studied. The characteristics are similar as the overall group, except that children have less exposure to cooking. Infiltration factor has significant effects on ambient source apportionment. Uncertainty associated with method, data, and results interpretation is discussed. Future work and policy making recommendations are made.