The impact of aerosol-radiation interactions on the effectiveness of emission control measures

Temporary emission control measures in Beijing and surrounding regions have become a prevailing practice to ensure good air quality for major events (e.g., the Asia-Pacific Economic Cooperation (APEC) Summit on 5-11 November 2014) and to mitigate the severity of coming pollution episodes. Since PM_2.5 affects meteorology via aerosol-meteorology interactions, a question arises how these interactions may impact the response of PM_2.5 to emission reductions and thus the effectiveness of emission control measures. Here we use the coupled meteorology-chemistry model WRF-Chem to investigate this issue with focus on aerosol-radiation interactions (ARI) for the APEC week and three more polluted episodes over North China. We find a quadratic relationship between PM_2.5 concentration changes due to emission reductions and PM_2.5 levels, instead of a linear response in the absence of ARI. The ARI effects could only change the effectiveness of emission control by 6.7% during APEC in Beijing, but reach 21.9% under more polluted conditions. Our results reveal that ARI can strongly affect the attribution of PM_2.5 variability to emission changes and meteorology, and is thus important for assessing the effectiveness of emission control measures.