Investigating the geographical heterogeneity in PM10-mortality associations in the China Air Pollution and Health Effects Study (CAPES): A potential role of indoor exposure to PM10 of outdoor origin

This study gives the first-time evidence for China that the geographical heterogeneity of the acute effects of outdoor PM10 can be partially explained by differences in indoor exposure to PM10 of outdoor origin. We used data from the China Air Pollution and Health Effects Study (CAPES), which demonstrated a geographical heterogeneity of the acute effect of particulate air pollution (particulate matter with an aerodynamic diameter smaller than 10 μm, or PM10) on mortality in 16 Chinese cities. Given that a large fraction of the exposure to PM10 of outdoor origin occurs indoors, we made the hypothesis that this heterogeneity might be partially explained by inter-city differences in indoor exposure to PM10 of outdoor origin. In our analysis, we estimated PM10 exposure coefficients (the change in the estimated personal exposure to PM10 of outdoor origin per unit change in outdoor PM10 concentration) in these 16 Chinese cities and examined their correlation with PM10 mortality coefficients (the increase in mortality associated with a given increase in the concentrations of outdoor PM10). We showed that the PM10 mortality coefficients and the PM10 exposure coefficients were significantly correlated, with an R-squared (R2) value of 0.549 (95% confidence interval: 0.201, 0.771; p < 0.01) for the 16 cities. The correlation was robust with different values of the key input parameters, and close in value to estimations found in previous studies on similar subjects.