Chemical drivers of ozone change in extreme temperatures in eastern China

Surface ozone pollution has become the biggest issue in China's air pollution since particulate matters have been improved in the atmosphere. Compared with normal winter/summer, extremely cold/hot weather sustained several days and nights by unfavorable meteorology is more impactful in this regard. However, ozone changes in extreme temperatures and their driving processes remain rarely understood. Here, we combine comprehensive observational data analysis and 0-D box models to quantify the contributions of different chemical processes and precursors to ozone change in these unique environments. Analyses of radical cycling indicate that temperature accelerates OH-HO₂-RO₂, optimizing ozone production efficiency in higher temperatures. The HO₂ + NO → OH + NO₂ reaction was the most influenced by temperature change, followed by OH + VOCs → HO₂/RO₂. Although most reactions in ozone formation increased with temperature, the increase in ozone production rates was greater than the rate of ozone loss, leading to a fast net ozone accumulation in heat waves. Our results also show that the ozone sensitivity regime is VOC-limited in extreme temperatures, highlighting the significance of volatile organic compound (VOC) control (particularly the control of alkenes and aromatics). In the context of global warming and climate change, this study helps us deeply understand ozone formation in extreme environments and design abatement policies for ozone pollution in such conditions.