Atmospheric oxidation capacity and O₃ formation in a coastal city of southeast China: Results from simulation based on four-season observation

The pollution of atmospheric ozone in China shows an obvious upward trend in the past decade. However, the studies on the atmospheric oxidation capacity and O 3 formation in four seasons in the southeastem coastal region of China with the rapid urbanization remain limited. Here, a four-season field observation was carried out in a coastal city of south -east China, using an observation-based model combining with the Master Chemical Mechanism, to explore the atmospheric oxidation capacity (AOC), radical chemistry, O 3 forma-tion pathways and sensitivity. The results showed that the average net O 3 production rate (14.55 ppbv/hr) in summer was the strongest, but the average O 3 concentrations in autumn was higher. The AOC and ROx levels presented an obvious seasonal pattem with the maximum value in summer, while the OH reactivity in winter was the highest with an average value of 22.75 sec-1 . The OH reactivity was dominated by oxygenated VOCs (OVOCs) (30.6%-42.8%), CO (23.2%-26.8%), NO2 (13.6%-22.0%), and alkenes (8.4%-12.5%) in different seasons. HONO photolysis dominated OH primary source on daytime in winter, while in other sea-sons, HONO photolysis in the morning and ozone photolysis in the aftemoon contributed mostly. Sensitivity analysis indicated that O 3 production was controlled by VOCs in spring, autumn and winter, but a VOC-limited and NOX-limited regime in summer, and alkene and aromatic species were the major controlling factors to O 3 formation. Overall, the study characterized the atmospheric oxidation capacity and elucidated the controlling factors for O 3 production in the coastal area with the rapid urbanization in China.(c) 2023 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.