To reduce air pollution within a 300 km radius from Hangzhou (the capital city of Zhejiang Province in East China) for the 2016 G20 summit (9/4-9/5), the 14-day (8/24-9/6) stringent pollution control measures were implemented in Shanghai. Changes in atmospheric concentrations during the same 14-day period from 2014 to 2016 were examined at two Supersites, i.e., urban Pudong site (PD) and Dianshan Lake regional site (DSL). Up to 50% reductions were found for PM2.5, with 13.1% and 9.7% reductions for SO2 and NO2, respectively. No apparent improvements were found for 8-h average O3 concentrations. Large reductions were also found for SO42- (51.4%), NO3- (68.8%), and NH4+ (84.4%), on average. Elevated coefficient of divergence values (0.52-0.56) suggested that pollutant sources differed at the two sites. Biomass burning, resuspended dust, combustion, iron and steel industry, sea salt, secondary aerosol, and vehicle exhaust were identified at the DSL site by Positive Matrix Factorization (PMF). Secondary aerosol and vehicle exhaust accounted for 45.7% of PM2.5 mass, followed 11.2%-13.7% each by industry, resuspended dust, and coal and oil combustion.