The impact of aerosol-radiation interaction and heterogeneous chemistry on the winter decreasing PM2.5 and increasing O3 in Eastern China 2014–2020

In the context of the prevalent winter air quality issues in China marked by declining PM2.5 and rising O3, this study employed a modified WRF-Chem model to examine the aerosol radiation interaction (ARI), heterogeneous chemistry (AHC), and their combined impact (ALL) on the variations in O3 and PM2.5 during the 2014–2020 in eastern China. Our analysis confirmed that ARI curtailed O3 while elevating PM2.5. AHC reduced O3 through heterogeneous absorption of NOx and hydroxides while notably fostering fine-grained sulfate, resulting in a PM2.5 increase. Emission reductions mitigated the inhibitory impact of ARI on meteorological fields and photolysis rates. Emission reduction individually without aerosol feedback led to a 5.43 ppb O3 increase and a 22.89 µg/m3 PM2.5 decrease. ARI and AHC amplified the emission-reduction-induced (ERI) O3 rise by 1.83 and 0.31 ppb, respectively. The response of ARI to emission diminution brought about a modest PM2.5 increase of 0.31 µg/m3. Conversely, AHC, acting as the primary contributor, caused a noteworthy PM2.5 decrease of 4.60 µg/m3. As efforts concentrate on reducing PM2.5, the promotion of ARI on PM2.5 counterbalanced the efficacy of emission reduction and the AHC-induced strengthening of PM2.5 decrease. The ALL magnified the ERI O3 increase by 38.9 % and PM2.5 decrease by 18.7 %. Sensitivity experiments with different degrees of emission reduction demonstrated a consistent linear relationship between the ALL-induced enhancement of O3 increase and PM2.5 decrease to the ERI PM2.5 decline. Our investigation revealed the complex connection between emissions and aerosol feedback in influencing air quality.