PNNL

Abstract

Surface fine particulate matter (PM2.5) pollution could be enhanced by feedback processes induced by aerosol-radiation interaction (ARI) and the aerosol-cloud interaction (ACI). Many previous studies have investigated the PM2.5 enhancements induced by ARI and ACI in China. However, few studies have examined the changes in the ARI- and ACI-induced PM2.5 enhancements over a long period, though the anthropogenic emissions have changed substantially in the last decade. In this study, we quantify the ARI- and ACI-induced PM2.5 enhancements in 2013 and 2021 using the Weather Research and Forecasting model with Chemistry (WRF-Chem) and investigate the driving factors for the changes. The results show that the PM2.5 enhancement induced by ARI in eastern China (5.59 µg m-3) is larger than that induced by ACI (3.96 µg m-3) in January 2013. However, the ACI-induced PM2.5 enhancement shows a significantly smaller decrease ratio (51%) than the ARI-induced enhancement (75%) for 2013–2021, making ACI more important for enhancing PM2.5 concentrations in January 2021. Anthropogenic emission reduction plays a key role in this shift. The decrease ratios of ACI-induced PM2.5 enhancement caused by the anthropogenic emission reduction (43% in January and 57% in July) are lower than those of the ARI-induced enhancements (57% in January and 67% in July). The primary reason for this phenomenon is that the decrease of ambient PM2.5 for 2013–2021 causes a disproportionately small decrease of liquid water path (LWP) under the condition of high PM2.5 concentration, therefore the surface solar radiation attenuation (and hence boundary layer height reduction) caused by ACI decreases slower than that caused by ARI. Moreover, the lower decrease ratio of the ACI-induced PM2.5 enhancement is dominated by the lower decrease ratio of ACI-induced secondary PM2.5 component enhancement, which is additionally caused by smaller decrease ratio of the air temperature reduction and relative humidity (RH) increase. Our findings reveal that with the decrease of ambient PM2.5, the ACI-induced PM2.5 enhancement inevitably becomes more important, which needs to be considered in the formulation of control policies to meet the national PM2.5 air quality standard.