Impact of China's Air Pollution Prevention and Control Action Plan on PM2.5 chemical composition over eastern China

China promulgated the Air Pollution Prevention and Control Action Plan(the Action Plan) in 2013 and developed stringent control measures to mitigate fine particulate matter(PMpollution.Here,we investigated the PMchemical composition changes over eastern China associated with the Action Plan during 2013-2017 using satellite-based PMchemical composition data derived using CMAQ simulations and satellite inputs.The PMconcentrations decreased considerably during this time as a result of the reductions in all chemical species in PM.The population-weighted mean concentrations over eastern China decreased from 11.1 to 6.7μgmfor SO,13.8-13.1μgmfor NO~-,7.4-5.8μgmfor NH~+,9.9-8.4μgmfor OM,4.6-3.8 μg mfor BC and 12.9-9.6 μg mfor other species in PM.SOhad the largest reduction of 40%,while NO~-had the lowest reduction of 5%,resulting in a greater fraction of NO~-and a smaller fraction of SOin PM.Among the three key regions,Beijing-Tianjin-Hebei had the largest reduction in PMand its chemical compositions.The decrease in SOconcentrations was in line with the reduction of SOemissions,and the major driver of the SOemission reductions was the industrial sector.The decrease in NOconcentrations was limited because the decrease in SOemissions and the stable NHemissions facilitated the formation of NO~- from HNO,which partialloffset the reduction in NOemissions driven by the power sector.To mitigate PMpollution more effectively,future efforts are needed to reduce NHemissions.