Enhanced PM_2.5 Decreases and O₃ Increases in China During COVID-19 Lockdown by Aerosol-Radiation Feedback

We apply an online-coupled meteorology-chemistry model (WRF-Chem) embedded with an improved process analysis to examine aerosol-radiation feedback (ARF) impacts on effectiveness of emission control due to Coronavirus Disease 2019 (COVID-19) lockdown over North China Plain. Emission reduction alone induces PM_2.5 decrease by 16.3 μg m^-3 and O₃ increase by 10.2 ppbv during COVID-19 lockdown. The ARF enhances PM_2.5 decrease by 2.7 μg m^-3 (16.6%) and O₃ increase by 0.8 ppbv (7.8%). The ARF-induced enhancement of PM_2.5 decline is mostly attributed to aerosol chemistry process, while enhancement of O₃ rise is ascribed to physical advection and vertical mixing processes. A set of sensitivity experiments with emission reductions in different degrees indicate that the ARF-induced enhancements of PM_2.5 declines (O₃ rises) follow a robust linear relationship with the emission-reduction-induced PM_2.5 decreases. The fitted relationship has an important implication for assessing the effectiveness of emission abatement at any extent.