Associations of particulate air pollution and daily mortality in 16 Chinese cities: an improved effect estimate after accounting for the indoor exposure to particles of outdoor origin.

People typically spend most of their time indoors. We modeled the daily indoor PM10 concentrations of outdoor origin using a set of exposure parameters, including the fraction of residences with air conditionings (AC), the fraction of time that windows are closed when cooling occurs for buildings with AC, the fractions of time that windows are open or closed for buildings with or without AC, the particle penetration factors, air change rates, and surface removal rate constant of PM10. We calculated the time-weighted average of the simulated indoor PM10 concentration of outdoor origin and the original recorded outdoor PM10 concentration. We then evaluated the acute effects of PM10 using traditional and amended exposure metrics in 16 Chinese cities. Compared with the original estimates, the new effect estimates almost doubled, with improved model fit and attenuated between-city heterogeneity. Conclusively, this proposed exposure assessment approach could improve the effect estimates of ambient particles.