Multi-pollutant air pollution and associated health risks in China from 2014 to 2020

We characterized air pollution over China during 2014-2020, with a novel focus on multi-pollutant air pollution (MPAP) for the first time (defined as co-pollution of two or more contaminants) which was quite common in China but has not been evaluated, and assessed associated health risks of air pollution exposure which specially took into account the effects of exposure to multi-pollutant mixture, by introducing a health-risk based and multi-pollutant air quality index (HAQI). High values of MPAP days were mostly distributed over North China with a 7-year average of 51.9 MPAP days. The severest MPAP occurred in winter with PM2.5-PM10 co-pollution accounting for 80-100% of MPAP days for six provinces of North China. One interesting phenomenon was that MPAP days exhibited almost overall declines (average trend of -11.9 days yr(-1)) over North China during 2014-2020 due to decreases in PM2.5-PM10 and PM2.5-O-3 co-pollution days, while single-pollutant air pollution (SPAP) days showed almost overall rising trends with an average trend of +8.0 days yr(-1) which was attributed to rapid increases in O-3 pollution days. The HAQI also exhibited high values over North China with a 7-year average HAQI value of 102.4. Health risks were the greatest in winter with 89.4% of population exposed to "unhealthy " air (HAQI > 100) and 20.1% of population suffering from "very unhealthy " (HAQI > 200) air over North China. Thanks to the mitigation of particulate pollution (shown as decreases in PM2.5 pollution days, PM2.5-PM10 co-pollution days, and PM2.5-O-3 co-pollution days), health risks in five provinces of North China except Shanxi experienced remarkable declines with HAQI trends of-3.1 yr(-1) -9.7 yr(-1) during 2014-2020. Unrelieved particulate pollution and deteriorating O-3 pollution, however, jointly led to rising health risks for Shanxi. These findings are expected to provide a scientific cognition of complex air pollution and associated health impacts.