Evidence for Reducing Volatile Organic Compounds to Improve Air Quality from Concurrent Observations and in Situ Simulations at 10 Stations in Eastern China

Ground-level ozone (O₃) has been an emerging air pollution in China and interacts with fine particulate matters (PM_2.5). We synthesized observations of O₃and its precursors in two summer months of 2020 at 10 sites in the Zhejiang province, East China and simulated the in situ photochemistry. O₃pollution in the northeastern Zhejiang province was more serious than that in the southwest. The site-average daytime O₃increment correlated well (R²= 0.73) with the total reactivity of volatile organic compounds (VOCs) and carbon monoxide toward the hydroxyl radical (OH) in urban areas. Model simulation revealed that the main function of nitrogen oxides (NO_x) at the rural sites where isoprene accounted for >85% of OH reactivity of VOCs was to facilitate the radical cycling. With NO_xreduction from 0 to 90%, the self-reactions between peroxy radicals (Self-Rxns), a proven pathway for secondary organic aerosol formation, were intensified by up to 23-fold in a NO_x-rich environment. In contrast, reducing VOCs could weaken the Self-Rxns while reducing O₃production rate and atmospheric oxidation capacity. This study observes and simulates O₃chemistry based on extensive measurements in typical Chinese cities, highlighting the necessity of reducing VOCs for co-benefit of O₃and PM_2.5