Impacts of implementing Healthy Building guidelines for daily PM limit on premature deaths and economic losses in urban China: A population-based modeling study.

Given a large fraction of people's exposure to urban PM occur indoors, reducing indoor PM levels may offer a more feasible and immediate way to save substantial lives and economic losses attributable to PM exposure. We aimed to estimate the premature mortality and economic loss reductions associated with achieving the newly established Chinese indoor air guideline and a few hypothetical indoor PM guideline values. We used outdoor PM concentrations from 1497 monitoring sites in 339 Chinese cities in 2015, coupled with a steady-state mass balance model, to estimate indoor concentrations of outdoor-infiltrated PM. Using province-specific time-activity patterns for urban residents, we estimated outdoor and indoor exposures to PM of outdoor origin. We then proceeded to use localized census-based concentration-response models and the value of statistical life estimates to calculate premature deaths and economic losses attributable to PM exposure across urban China. Finally, we estimated potentially avoidable mortality and corresponding economic losses by meeting the current 24-hour based guideline and various hypothetical indoor limits for PM. In 2015 in urban areas of mainland China, the city-specific annual mean outdoor and indoor PM concentrations ranged 9-108 μg/m and 5-56 μg/m, respectively. Indoor exposures contributed 62%-91% daily and 68%-83% annually to the total time-weighted exposures. The potential reductions in total deaths and economic losses for the scenario in which daily indoor concentrations met the current guideline of 75 μg/m, 37.5 μg/m, and 25 μg/m were 16.9 (95% CI: 0.7-62.1) thousand, 87.7 (95% CI: 9.7-197.7) thousand, and 165.5 (95% CI: 30.8-304.0) thousand, respectively. The corresponding reductions in economic losses were 5.7 (95% CI: 0.2-34.8) billion, 29.4 (95% CI: 2.4-109.6) billion, and 55.2 (95% CI: 7.7-168.0) billion US Dollars, respectively. Deaths and economic losses would be reduced exponentially within the range of 0-75 μg/m for hypothetical indoor PM limits. The findings demonstrate the effectiveness of reducing indoor concentrations of outdoor-originated PM in saving substantial lives and economic losses in China. The analysis provides quantitative evidence to support the implementation of an indoor air quality guideline or standard for PM.