资源环境科技发展态势分析平台

High levels of secondary air pollutants during COVID‐19 in China have aroused great concern. In Beijing, measured daily mean peroxyacetyl nitrate (PAN) concentrations reached 4 ppb over the lockdown period (01/24−02/15), whose averages were 2−3 times that before lockdown (01/01−01/23). The lockdown PAN levels also reached a high historical record based on our long‐term measurements (2016−2019). Unlike ozone and PM_2.5, PAN formation depends on less complex photochemistry between NO_x and volatile organic compounds (VOCs), providing a novel approach to investigate the wintertime photochemistry during COVID‐19. The GEOS‐Chem simulations suggest a markedly enhanced photochemistry by a factor of 2 during the lockdown. Change of meteorology featuring with anomalous wind convergence under higher temperatures is the main reason for enhanced photochemical formation of PAN, while chemically nonlinear feedbacks also play a role. Our results suggest implementing targeted VOC emission controls in the context of increasing photochemical pollution over this complex polluted region.