title: Modifications of exposure to ambient particulate matter: Tackling bias in using ambient concentration as surrogate with particle infiltration factor and ambient exposure factor.
abstract: Numerous epidemiological studies explored health risks attributed to outdoor particle pollution. However, a number of these studies routinely utilized ambient concentration as a surrogate for personal exposure to ambient particles. This simplification ignored the difference between indoor and outdoor concentrations of outdoor originated particles and may bias the estimate of particle-health associations. Intending to avoid the bias, particle infiltration factor (Finf), which describes the penetration of outdoor particles in indoor environment, and ambient exposure factor (α), which represents the fraction of outdoor particles people are truly exposed to, are utilized as modification factors to modify outdoor particle concentration. In this study, the probabilistic distributions of annually-averaged and seasonally-averaged Finfand α were assessed for residences and residents in Beijing. Finfof a single residence and α of an individual was estimated based on the mechanisms governing particle outdoor-to-indoor migration and human time-activity pattern. With this as the core deterministic model, probabilistic distributions of Finfand α were estimated via Monte Carlo Simulation. Annually-averaged Finfof PM2.5and PM10for residences in Beijing tended to be log-normally distributed as lnN(-0.74,0.14) and lnN(-0.94,0.15) with geometric mean value as 0.47 and 0.39, respectively. Annually-averaged α of PM2.5and PM10for Beijing residents also tended to be log-normally distributed as lnN(-0.59,0.12) and lnN(-0.73,0.13) with geometric mean value as 0.55 and 0.48, respectively. As for seasonally-averaged results, Finfand α of PM2.5and PM10were largest in summer and smallest in winter. The obvious difference between these modification factors and unity suggested that modifications of ambient particle concentration need to be considered in epidemiological studies to avoid misclassifications of personal exposure to ambient particles. Moreover, considering the inter-individual difference of Finfand α may lead to a brand new perspective of particle-health associations in further epidemiological study.
authors.affiliation: Department of Building Science, School of Architecture, Tsinghua University, Beijing 100084, PR China.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Shi
authors.affiliation: Department of Building Science, School of Architecture, Tsinghua University, Beijing 100084, PR China.
authors.forename: Chen
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Building Science, School of Architecture, Tsinghua University, Beijing 100084, PR China; Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, China. Electronic address: binzhao@tsinghua.edu.cn.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhao
mesh_terms: D000392:Air Movements; D016902:Air Pollution, Indoor / Q000032:analysis*; D000068476:Beijing; D004784:Environmental Monitoring / Q000379:methods*; D006798:Housing; D006801:Humans; D008962:Models, Theoretical; D009010:Monte Carlo Method; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D012621:Seasons
chemical_list: D052638:Particulate Matter
keywords: Ambient exposure factor; Ambient particle pollution; Indoor air; Infiltration factor; Personal exposure; Probabilistic distribution