Impact of emission reduction on aerosol-radiation interaction during heavy pollution periods over Beijing-Tianjin-Hebei region in China

In December 2015,the Beijing-Tianjin-Hebei(BTH) region experienced several episodes of heavy air pollution.The government immediately issued emergency control measures to reduce the pollution,which provided a good opportunity to explore the impact of emission reduction on aerosol-radiation interaction.In this study,four tests were conducted,including the basel simulation with emission reduction and aerosol-radiation interaction on,the base2 simulation with emission reduction and aerosol-radiation interaction off,the scenariol simulation without emission reduction and aerosol-radiation interaction on and the scenario2 simulation without emission reduction and aerosol-radiation interaction off.We find that the aerosol-radiation interaction decreased the downward shortwave radiation and the temperature at 2 m,reduced the planetary boundary layer height(PBLH) in the region,and increased the relative humidity at 2 m,which is favorable for pollution accumulation.Our results revealed that the interaction effect due to emission reductions increased downward shortwave radiation by an average of 0-5 W/m2,leading to increase in surface temperature of 0-0.05℃,increase in the daytime mean PBL high of 0-8 m,and decrease in daytime mean relative humidity at 2 m of 0.5%.We found that if there were aerosol-radiation interaction,it would enhance the effectiveness of emission control measures on air pollution control.The enhance of PM2.5(particulate matter less than 2.5 um),PM10(particulate matter less than 10 um),and NO2(nitrogen dioxide) emission reduction effects reached7.62%,6.90%,11.62%,respectively,over this region.