Ground-level ozone (O3) pollution remains persistently high in China, despite the implementation of rigorous emission reduction measures targeting primary pollutants. The atmospheric oxidation capacity (AOC) serves as an essential driving force for O3 formation; yet, its underlying mechanism is still not fully elucidated. Herein, we conducted a one-year observation campaign in Hangzhou, China, to characterize the temporal variations in O3, and to clarify the drivers and reaction mechanisms of AOC, ROx· radicals, and O3 formation. We found that the maximum O3 concentrations occurred in summer, during which the average AOC value (2.01 ± 2.85 × 107 molecules cm–3 s–1) was 2.4–6 times higher than in other seasons. Daytime AOC was driven by the hydroxyl radical (OH·, 83.00%–95.20%), which was itself generated mainly through O3 photolysis in all seasons except winter. Furthermore, nitrogen oxide (NOx) and relative humidity (RH) were identified as the principal individual factors controlling O3 formation of the 3 under low and moderate AOC scenarios, whereas the temperature–NOx interaction and temperature-oxygenated volatile organic compounds (OVOCs) interaction emerged as the most critical factors under moderate and high AOC conditions, respectively. Our findings highlight the importance of devising O3 mitigation strategies that account for AOC dynamics and multipollutant interactions, thereby supporting the development of tailored, region-specific control measures.
Li et al. (2026) studied this question.