Impacts of short-Term mitigation measures on PM2.5 and radiative effects: A case study at a regional background site near Beijing, China

Measurements at a background site near Beijing showed that pollution controls implemented during the 19th National Congress of the Communist Party of China (NCCPC) were effective in reducing PM _2:5 . Mass concentrations of PM _2:5 and its major chemical components were 20.6%-43.1% lower during the NCCPC-control period compared with a non-control period, and differences were greater on days with stable meteorological conditions. A receptor model showed that PM _2:5 from traffic-related emissions, biomass burning, industrial processes, and mineral dust was 38.5 %-77.8% lower during the NCCPC-control versus noncontrol period, but differences in PM _2:5 from coal burning were small, and secondary sources were higher during the NCCPC-control period. During one pollution episode in the non-control period, secondary sources dominated, and the WRF-Chem model showed that the Beijing-Tianjin-Hebei (BTH) region contributed 73.6% of PM _2:5 mass. A second pollution episode was linked to biomass burning, and BTH contributed 46.9% of PM _2:5 mass. Calculations based on Interagency Monitoring of Protected Visual Environments (IMPROVE) algorithms showed that organic matter was the largest contributor to light extinction during the non-control period whereas NH ₄ NO ₃ was the main contributor during the NCCPC. The Tropospheric Ultraviolet and Visible radiation model showed that the average direct radiative forcing (DRF) values at the Earth's surface were-14:0 and-19:3Wm ^-2 during the NCCPC-control and non-control periods, respectively, and the DRF for the individual PM _2:5 components were 22.7 %-46.7% lower during the NCCPC. The information and dataset from this study will be useful for developing air pollution control strategies in the BTH region and for understanding associated aerosol radiative effects.