Hourly-Resolved temperature inflection points of ozone formation: Chemical pathways and precursor sensitivity in Zhengzhou, China

Abstract. Ground-level ozone (O₃) is a key secondary pollutant. Its formation is nonlinearly modulated by temperature, an effect amplified under climate warming. However, the chemical mechanisms by which temperature influences the diurnal O₃ cycle and its synergistic interactions with other parameters remain inadequately understood. By integrating observational data from a typical inland city in China with model simulations and machine learning, this study identifies the temperature inflection point for O₃ formation and elucidates the underlying chemical mechanisms and dominant controlling factors. The net O₃ production rate (P_net(O₃)) peaks at 31 °C. The rapid formation between 25 and 31 °C is driven by the HO₂+NO and RO₂+NO pathways, with enhanced nitrogen dioxide photolysis rate (J(NO₂)) and elevated isoprene as the main drivers. From 31 to 36 °C, P_net(O₃) declines because the HO₂+NO pathway is weakened and decreasing photolysis rates become the dominant limiting factor. Above 36 °C, nitrous acid (HONO) and formaldehyde (HCHO) concentrations decrease, weakening radical cycling and further suppressing O₃ formation. Sensitivity and two-factor analyses support a temperature-dependent dynamic control strategy: in the low-temperature range (22–31 °C), priority should be given to controlling anthropogenic alkenes with nitrogen oxides (NO_x) reductions to avoid diminishing returns from single-species cuts; in the high-temperature range (32–40 °C), NO_x reductions should be intensified, and synergistic precursors such as HONO and oxygenated volatile organic compounds (OVOCs) should be reduced with emphasis, enhancing the O₃ reduction benefit per unit emission and mitigating O₃ pollution risks under a warming climate.