Investigating factors causing difference of indoor exposure to outdoor PM2.5-bounded elemental carbon during different seasons and haze/non-haze days using a Monte Carlo framework

Abstract

To assess the factors influencing indoor exposure from outdoor PM2.5-bounded elemental carbon (EC), we developed a Monte Carlo framework to investigate the ambient exposure factor (the ratio of exposure concentration to ambient concentration) of PM2.5-bounded EC. The framework integrates outdoor PM2.5-bounded EC concentrations, the probability of window opening, dependence on outdoor parameters (temperature, humidity, wind speed, PM2.5 concentration), EC infiltration factors, and population time-activity patterns. We investigated the population exposure in Beijing, which suffers from heavy air pollution, from January 1, 2013 to December 31, 2015. The average population exposure to outdoor PM2.5-bounded EC modified by ambient exposure factor was 2.24 μg/m3 (95% confidence interval (CI):1.06–4.30 μg/m3) in winter, 1.91 μg/m3 (CI:1.43–2.74 μg/m3) in the transition seasons, 1.53 μg/m3 (CI:1.51–1.56 μg/m3) in summer, 2.92 μg/m3 (CI:2.02.–4.53 μg/m3) on haze days, and 1.02 μg/m3 (CI:0.82–1.39 μg/m3) on non-haze days. Increases in outdoor temperature and humidity increased ambient exposure factors, whereas an increase in outdoor PM2.5 concentration decreased the ratio of exposure concentration to ambient concentration. This implies that lower temperatures in winter and higher PM2.5 concentrations on haze days result in a population exposure to a lower proportion of outdoor PM2.5-bounded EC.