Accelerated reduction of air pollutants in China, 2017-2020
Emission regulations of the power and industry sectors have been identified as the major driver of PM2.5 mitigation over China during 2013-2017. In this study, we use ground-based observations of four air pollutants (CO, NO2, SO2, and PM2.5) to show that additional stringent emission policies on the industrial, transportation, and residential sectors during the new 3-year protection plan (2018-2020) have accelerated the improvement of China's air quality. Based on regional (North and South China) trends of annual mean measurements, significant reductions are observed for all four pollutants during 2017-2020. These decreasing trends are found to be >30% stronger than 2015-2017 for NO2, CO, and PM2.5. For CO and PM2.5, the acceleration is the strongest in winter and North China, when and where the residential clean-heating actions were implemented. While for NO2, the accelerations are pronounced regardless of region or season, reflecting nationwide measures to reduce NOx emissions from industrial and transportation activities. SO2 concentration reductions that were already substantial before 2017 are maintained but not accelerated, consistent with the dominance of end-of-pipe measures rather than a structural change of energy fuels. Our investigation highlights the value of multi-pollutant analysis to relate emission policies with air quality changes.