Exploring the role of aerosol-ozone interactions on O₃ surge and PM_2.5 decline during the clean air action period in Eastern China 2014-2020

The China implemented the Clean Air Action Plan (CAAP) in September 2013 to address the pressing air pollution problem. This initiative yielded a noteworthy reduction in PM2.5 while simultaneously witnessing the O-3 elevation. Here, we used a revised WRF-Chem model to study the drivers (anthropogenic emissions (EMI), meteorological changes (MET)) of decreasing PM2.5 and increasing O-3 in eastern China across the four seasons from 2014 to 2020, focusing on the response of aerosol-ozone interaction (AOI) to emission reduction (AOI_ER). In contrast to the original version, the model provided more comprehensive feedback of aerosols on O-3, including radiation effects and heterogeneous chemistry. Our survey showed that EMI was the main factor causing the PM2.5 decline and O-3 increase. The influence of MET on both O-3 and PM2.5 exhibited seasonal variations. Compared to 2014, emission reduction during CAAP weakened the inhibition of aerosol radiative effect on meteorological parameters and photolysis rate, causing a rise in surface shortwave radiation (SW), temperature (T-2), planetary boundary layer height (PBLH), wind speed (WS10), J(NO2), and J(O1D) throughout the CAAP period. This increased the O-3 by 0.57-2.11 ppb in the four seasons and enhanced the emission-reduction-induced O-3 increase by 22.2%-57.3%. Emission reduction alleviated the summer negative feedback of AOI on PM2.5, increasing by 4.61 mu g m(-3), thereby offsetting the 16.7% emission reduction efficacy. Oppositely, in spring, autumn, and winter, emission reduction weakened the promotion of AOI on PM2.5, resulting in a decrease by 2.5-3.12 mu g m(-3), amplified the emission-reduction-induced PM2.5 reduction by 8.3%-26.6%. Nitrate and sulfate aerosols generated by heterogeneous chemistry emerged as the primary components driving the alterations in PM2.5 within the context of emission reduction. Our research emphasized the importance of considering changes in AOI when formulating emission control policies and evaluating their effectiveness. More effective emission policies should focus on comprehensively considering the emissions and the weakened aerosol effects to achieve better air quality and health benefits.