Deaths Attributable to Indoor PM2.5 in Urban China When Outdoor Air Meets 2021 WHO Air Quality Guidelines

The World Health Organization reduced the recommended level of annual mean PM2.5 concentrations to 5 mu g/m3 in 2021. Previously, the guideline was geared toward ambient air pollution, and now it explicitly applies to indoor air pollution. However, the disease burden attributed to different indoor emission sources has been overlooked, particularly in urban areas. Our objective was to estimate the mortality attributable to indoor PM2.5 in urban areas in China. Our model estimated 711 thousand (584-823) deaths and 2.75 trillion (2.26-3.19) CNY economic losses attributable to PM2.5 in urban China in 2019, in which indoor sources contributed 394 thousand (323-457) deaths and 1.53 trillion (1.25-1.77) CNY losses. There would still be 536 thousand (427-638) PM2.5-attributable deaths and 2.07 trillion (1.65-2.47) CNY losses each year when the outdoor PM2.5 is 5 mu g/m3, of which 485 thousand (386-578) deaths and 1.87 trillion (1.49-2.23) CNY are attributable to indoor sources. Despite cleaner outdoor air and no solid fuels being used, considerable health hazards and economic losses are attributable to indoor PM2.5. Measures to reduce PM2.5 exposure in humans from both indoor and outdoor sources are to achieve a substantial reduction in deaths.