The Impact of Extreme Summer Heat on VOC Sensitivity and Ozone Formation: Insights From Field Campaigns in a Sichuan Basin Megacity, China

Regional photochemical pollution remains a major issue in many of China's megacities, characterized by persistently high ozone (O 3 ) concentrations and an expanding polluted area. In the summer of 2022, several cities in China experienced prolonged regional O 3 pollution, exacerbated by heat waves. As heat waves events become more frequent, the influence of meteorological factors on O 3 pollution has gained greater attention. This study, based on observational data from summer campaigns (July and August) in 2021 and 2022 in Chengdu, a megacity in the Sichuan Basin, investigated O 3 formation sensitivity to meteorological parameters such as temperature, relative humidity, and solar radiation (represented by the photolysis coefficient of NO 2 ). In August 2022, the urban area of Chengdu experienced its hottest month in nearly 20 years, with maximum temperatures reaching 41.6°C. By calculating the photochemical initial concentrations (PICs) of volatile organic compounds (VOCs) to assess O 3 reactivity, we found that summer O 3 formation in Chengdu operated under a transitional regime, colimited by both VOCs and NOx. An observation‐based box model, using PIC data, further demonstrated that during the heat waves of 2022, O 3 peak values increased by 31.4% compared to 2021. Additionally, when solar radiation increased by 10% from average to maximum values, O 3 peak levels rose by approximately 9%, highlighting the significant effect observed. Heat waves could increase the emission and reactivity of certain VOCs, particularly from solvent use and vehicular exhaust, such as m/p‐xylene, trans‐2‐butene, and trans‐2‐pentene. These findings enhance our understanding of how extreme weather influences O 3 pollution and provide valuable insights for future control strategies.