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 (PM2.5) pollution. Here, we investigated the PM2.5 chemical composition changes over eastern China associated with the Action Plan during 2013-2017 using satellite-based PM2.5 chemical composition data derived using CMAQ simulations and satellite inputs. The PM2.5 concentrations decreased considerably during this time as a result of the reductions in all chemical species in PM2.5. The population-weighted mean concentrations over eastern China decreased from 11.1 to 6.7 mu g m(-3) for SO42-\documentclass[12pt]end, 13.8-13.1 mu g m(-3) for NO3-\documentclass[12pt], 7.4-5.8 mu g m(-3) for NH4+\documentclass[12pt], 9.9-8.4 mu g m(-3) for OM, 4.6-3.8 mu g m(-3) for BC and 12.9-9.6 mu g m(-3) for other species in PM2.5. SO42-\documentclass[12pt] had the largest reduction of 40%, while NO3-\documentclass[12pt] had the lowest reduction of 5%, resulting in a greater fraction of NO3-\documentclass[12pt]and a smaller fraction of SO42-\documentclass[12pt] in PM2.5. Among the three key regions, Beijing-Tianjin-Hebei had the largest reduction in PM2.5 and its chemical compositions. The decrease in SO4 2 concentrations was in line with the reduction of SO2 emissions, and the major driver of the SO2 emission reductions was the industrial sector. The decrease in NO3-\documentclass[12pt] concentrations was limited because the decrease in SO2 emissions and the stable NH3 emissions facilitated the formation of NO3-\documentclass[12pt] from HNO3, which partially offset the reduction in NOx emissions driven by the power sector. To mitigate PM2.5 pollution more effectively, future efforts are needed to reduce NH3 emissions.