Estimation of infiltration efficiency of ambient PM2.5 in urban residences of Beijing during winter

Fine particulate matter pollution has become a major public health concern in the urban areas of China. Ambient PM2.5 concentrations measured at fixed sites are commonly used as an exposure surrogate, although exposure to ambient PM2.5 primarily occurs in indoor environments. In this study, valid indoor and outdoor mass concentrations of PM2.5 during winter, were concurrently measured in 26 urban residences in Beijing. The infiltration factor (Finf), defined as the fraction of ambient PM2.5 which penetrates indoors and remains suspended, was estimated using a recursive model. The environmental conditions that significantly influenced Finf were screened using a general linear model and multiple regression analysis. Finf during winter was 0.52 +/- 0.25 with large home-by-home variability. The results suggested that: (1) infiltration from outdoor to indoor environments remarkably reduced the concentrations of ambient PM2.5; and (2) using ambient PM2.5, as an exposure surrogate, can result in exposure misclassification. Improved ventilation was found to increase Finf, whereas an increase in indoor RH from 19.20 to 51.30% resulted in a reduction in Finf. The residences proximate to arterial roads were found to be prone for the infiltration of ambient PM2.5. There were remarkable seasonal differences in the infiltration behavior of ambient PM2.5.