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Estimating In-Vehicle Concentration of and Exposure to Fine Particulate Matter

Fine particulate matter (PM2.5) exposure is associated with short-term and chronic respiratory effects. It is necessary to investigate human exposure to PM2.5 to support the 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 for in-vehicle PM2.5 concentration is reviewed. An alternative approach for 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 to estimate in-vehicle concentration, has been specified and applied. The objectives of this paper are to (a) demonstrate the application of the alternative approach to various scenarios, (b) analyze the sensitivity of the modeling results to the key inputs, and (c) evaluate this approach. Typical inputs for the alternative approach are reviewed. Sensitivities of these inputs to the modeling results and estimated human exposure have been analyzed. The in-vehicle PM2.5 concentration was estimated to vary by more than a factor of two, depending on factors such as the cabin air exchange rate and filter efficiency of the ventilation system. Recommendations are made for field data that would be useful to better characterize variability in factors that affect in-vehicle PM2.5 concentration.