Reducing Indoor Levels of “Outdoor PM_2.5” in Urban China: Impact on Mortalities

This study estimates adult mortalities attributed to PM_2.5 across urban China in 2015 and the corresponding mortalities that might be avoided by meeting the yearly averaged indoor PM_2.5 threshold in the newly established Assessment Standard for Healthy Building (ASHB) and seven other potential thresholds. We use outdoor PM_2.5 concentrations from ∼1500 monitoring sites in 339 Chinese cities, coupled with a detailed exposure model, to estimate outdoor and indoor exposures to PM_2.5 originating outdoors. We proceed to calculate premature mortality attributable to PM_2.5 exposure using an integrated exposure-response model. Results indicate that indoor exposures accounted for 66%–87% of total exposure to PM_2.5 of outdoor origin and 81% (95% confidence interval (CI), 71%–87%), i.e., 316 000 (95% CI, 176 000–435 000), of the 389 000 (95% CI, 245 000–501 000) mortalities attributable to “outdoor PM_2.5” for the urban population ≥25 years of age in China in 2015. Potentially 14 000 (95% CI, 8000–20 000) deaths might be avoided if indoor PM_2.5 of outdoor origin met the ASHB guideline of 35 μg/m³ for annual mean indoor PM_2.5, and 162 000 (95% CI, 79 000–237 000) deaths might be avoided by meeting a 10 μg/m³ threshold. The analysis in this work should be helpful in formulating indoor air quality policies.