Temporal variations and spatial distributions of gaseous and particulate air pollutants and their health risks during 2015–2019 in China

Air quality has been significantly improved in China in recent years; however, our knowledge of the long-term changes in health risks from exposure to air pollutants remain less understood. Here we investigated the temporal variations and spatial distributions of six criteria pollutants (SO2, NO2, O3, CO, PM2.5 and PM10) in Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD) during 2015-2019. SO2 showed 36-60% reductions in three regions, comparatively, NO2 decreased by 3-17% in BTH and YRD and had a 5% increase in PRD. PM2.5 and PM10 showed the largest reductions in BTH (30-33%) and the lowest in PRD (7-13%), while O3 increased by 9% during 2015-2019 particularly in BTH and YRD. Assuming that only air pollutants above given thresholds exert excess risk (ERtotal) of mortality, we found that the different variations of pollutants have caused ERtotal in BTH decreasing significantly from 4.8% in 2015 to 2.0% in 2019, while from 1.9% to 1.0% in YRD, and a small change in PRD. These results indicate substantially decreased health risks of mortality from exposure to air pollutants as a response to improved air quality. Overall, PM2.5 dominated ERtotal accounting for 42-53% in BTH and 58-64% in YRD with steadily increased contributions, yet ERtotal presented strong seasonal dependence on air pollutants with largely increased contribution of O3 in summer. The ERtotal caused by SO2 was decreased substantially and became negligible except in winter in BTH, while NO2 only played a role in winter. We also found that ERPM2.5 was compositional dependent with organics being the major contributor at low ERPM2.5 while nitrate was more important at high ERPM2.5. Our results highlight that evaluation of public health risks of air pollution needs to consider chemical differences of PM in different regions in addition to dominant air pollutants in different seasons.