@article{liu_frey_2011, title={Modeling of in-vehicle human exposure to ambient fine particulate matter}, volume={45}, ISSN={["1873-2844"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79960586024&partnerID=MN8TOARS}, DOI={10.1016/j.atmosenv.2011.04.019}, abstractNote={A method for estimating in-vehicle PM2.5 exposure as part of a scenario-based population simulation model is developed and assessed. In existing models, such as the Stochastic Exposure and Dose Simulation model for Particulate Matter (SHEDS-PM), in-vehicle exposure is estimated using linear regression based on area-wide ambient PM2.5 concentration. An alternative modeling approach is explored based on estimation of near-road PM2.5 concentration and an in-vehicle mass balance model. Near-road PM2.5 concentration is estimated using a dispersion model and fixed site monitor (FSMs) data. In-vehicle concentration is estimated based on air exchange rate and filter efficiency. In-vehicle concentration varies with road type, traffic flow, windspeed, stability class, and ventilation. Average in-vehicle exposure is estimated to contribute 10–20 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.}, number={27}, journal={ATMOSPHERIC ENVIRONMENT}, author={Liu, Xiaozhen and Frey, H. Christopher}, year={2011}, month={Sep}, pages={4745–4752} }
 @article{liu_frey_cao_2010, title={Estimating In-Vehicle Concentration of and Exposure to Fine Particulate Matter Near-Roadway Ambient Air Quality and Variability in Vehicle Operation}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78651334013&partnerID=MN8TOARS}, DOI={10.3141/2158-13}, abstractNote={ 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. }, number={2158}, journal={TRANSPORTATION RESEARCH RECORD}, author={Liu, Xiaozhen and Frey, H. Christopher and Cao, Ye}, year={2010}, pages={105–112} }