@article{jiao_frey_cao_2012, title={Assessment of Inter-Individual, Geographic, and Seasonal Variability in Estimated Human Exposure to Fine Particles}, volume={46}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84869388772&partnerID=MN8TOARS}, DOI={10.1021/es302803g}, abstractNote={Health effects associated with ambient fine particle (PM(2.5)) exposure are typically estimated based on concentration-response (C-R) functions using area-wide concentration as an exposure surrogate. Persons 65 and older are particularly susceptible to adverse effects from PM(2.5) exposure. Using a stochastic microenvironmental simulation model, distributions of daily PM(2.5) exposures were estimated based on ambient concentration, air exchange rate, penetration factor, deposition rate, indoor emission sources, census data, and activity diary data, and compared for selected regions and seasons. Even though the selected subpopulation spends an average of over 20 h per day indoors, the ratio of daily average estimated exposure to ambient concentration (E(a)/C) is approximately 0.5. The daily average E(a)/C ratio varies by a factor of 4-5 over a 95% frequency range among individuals, primarily from variability in air exchange rates. The mean E(a)/C varies by 6-36% among selected NC, TX, and NYC domains, and 15-34% among four seasons, as a result of regional differences in housing stock and seasonal differences in air exchange rates. Variability in E(a)/C is a key factor that may help explain heterogeneity in C-R functions across cities and seasons. Priorities for improving exposure estimates are discussed.}, number={22}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Jiao, Wan and Frey, H. Christopher and Cao, Ye}, year={2012}, month={Nov}, pages={12519–12526} }
 @article{cao_frey_2012, title={Modeling of Human Exposure to In-Vehicle PM2.5 from Environmental Tobacco Smoke}, volume={18}, ISSN={["1549-7860"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84861953590&partnerID=MN8TOARS}, DOI={10.1080/10807039.2012.672894}, abstractNote={ABSTRACT Environmental tobacco smoke (ETS) is estimated to be a significant contributor to in-vehicle human exposure to fine particulate matter of 2.5 μm or smaller (PM2.5). A critical assessment was conducted of a mass balance model for estimating PM2.5 concentration with smoking in a motor vehicle. Recommendations for the range of inputs to the mass-balance model are given based on literature review. Sensitivity analysis was used to determine which inputs should be prioritized for data collection. Air exchange rate (ACH) and the deposition rate have wider relative ranges of variation than other inputs, representing inter-individual variability in operations, and inter-vehicle variability in performance, respectively. Cigarette smoking and emission rates and vehicle interior volume are also key inputs. The in-vehicle ETS mass balance model was incorporated into the Stochastic Human Exposure and Dose Simulation for Particulate Matter (SHEDS-PM) model to quantify the potential magnitude and variability of in-vehicle exposures to ETS. The in-vehicle exposure also takes into account near-road incremental PM2.5 concentration from on-road emissions. Results of probabilistic study indicate that ETS is a key contributor to the in-vehicle average and high-end exposure. Factors that mitigate in-vehicle ambient PM2.5 exposure lead to higher in-vehicle ETS exposure, and vice versa.}, number={3}, journal={HUMAN AND ECOLOGICAL RISK ASSESSMENT}, author={Cao, Ye and Frey, H. Christopher}, year={2012}, pages={608–626} }
 @article{cao_frey_2011, title={Geographic differences in inter-individual variability of human exposure to fine particulate matter}, volume={45}, ISSN={["1352-2310"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80052319017&partnerID=MN8TOARS}, DOI={10.1016/j.atmosenv.2011.07.034}, abstractNote={Human exposure to fine particulate matter (PM2.5) is associated with short and long term adverse health effects. The amount of ambient PM2.5 that infiltrates indoor locations such as residences depends on air exchange rate (ACH), penetration factor, and deposition rate. ACH varies by climate zone and thus by geographic location. Geographic variability in the ratio of exposure to ambient concentration is estimated based on comparison of three modeling domains in different climate zones: (1) New York City; (2) Harris County in Texas, and (3) a six-county domain along the I-40 corridor in North Carolina. Inter-individual variability in exposure to PM2.5 was estimated using the Stochastic Human Exposure and Dose Simulation for Particulate Matter (SHEDS-PM) model. ACH is distinguishably the most sensitive input for both ambient and non-ambient exposure to PM2.5. High ACH leads to high ambient exposure indoors but lower non-ambient exposure, and vice versa. For summer, the average ratio of exposure to ambient concentration varies by 13 percent among the selected domains, mainly because of differences in housing stock, climate zone, and seasonal ACH. High daily average exposures for some individuals are mainly caused by non-ambient exposure to smoking or cooking. The implications of these results for interpretation of epidemiological studies are discussed.}, number={32}, journal={ATMOSPHERIC ENVIRONMENT}, author={Cao, Ye and Frey, H. Christopher}, year={2011}, month={Oct}, pages={5684–5691} }
 @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} }