Tightening Standards for Indoor Levels of PM2.5: A Promising Approach for Reducing PM2.5 Associated Mortalities in Urban China

Abstract

Outdoor PM2.5 pollution in China has been estimated to cause more than one million premature mortalities annually. In urban areas residents spend a major fraction of their time indoors, meaning that a large fraction of urban exposure to “outdoor PM2.5” occurs indoors. This study estimates premature adult mortalities attributed to PM2.5 across urban China in 2015 and the corresponding mortality reductions achieved by meeting the yearly-averaged indoor PM2.5 threshold in the newly established Assessment Standard for Healthy Building (ASHB) and seven other potential thresholds. We use outdoor PM2.5 concentrations from 1497 monitoring sites in 366 cities in China, coupled with a detailed exposure model, to estimate outdoor and indoor exposures to PM2.5 originating outdoors. We proceed to calculate premature mortality attributable to PM2.5 exposure using an integrated exposure-response model. Results indicate that indoor exposures accounted for 66%-87% of total exposure to PM2.5 of outdoor origin and 76% (248,174) of the 328,362 premature mortalities attributable to “outdoor PM2.5” for the urban population ≥25 years of age in China in 2015. Stroke, ischemic heart disease, chronic obstructive pulmonary disease, and lung cancer mortalities attributable to indoor exposure were 132,209, 71,960, 24,233 and 19,773, respectively. Potentially 10,172 deaths could be avoided if indoor PM2.5 of outdoor origin met the current ASHB standard of 35 μg/m3 as annual mean, and 113,219 deaths could be avoided by meeting a 10 μg/m3 threshold. The findings demonstrate the effectiveness of reducing indoor exposures to “outdoor PM2.5” in reducing premature mortalities attributable to urban PM2.5 pollution in China. Estimates of mortality reductions associated with various indoor PM2.5 thresholds can help formulate indoor air quality policies and practices, including building- or room-based filtration of ventilation air.