Effects of heat waves on ozone pollution in a coastal industrial city: Meteorological impacts and photochemical mechanisms

Surface ozone (O₃) pollution triggered by extreme weather conditions is attracting increasing attention. Heat waves in summer of 2022 were chosen to explore the photochemical and meteorological impacts on O₃ formation in the southeastern coastal industrial city of Quanzhou in China. The machine-learning (ML)-based weather normalization showed that the de-weathered O₃ concentrations (increased by 6.69 μg m⁻³) in 2022 were higher than those from 2015 to 2021. Temperature is the most important variable (33.5%), followed by solar radiation (23.5%) and RH (10.1%), differing from the O₃ pollution in inland cities. The Observation-Based Model (OBM) analysis results showed that hydroxyl radical (OH) was the predominant oxidant for daytime atmospheric oxidation capacity (AOC). And oxygenated volatile organic compounds (OVOCs), NO₂, and CO were the dominant contributors to OH reactivity, accelerating the recycling of ROx radicals and O₃ formation. The daytime reaction rate of HO₂+NO during the O₃ pollution episodes was 20.0 ppb h⁻¹, accounting for 65% of the total O₃ production. The contribution of RO₂+NO to the O₃ production enhanced the possibility of the MDA8h O₃ exceeding the Air Quality Standard of China. This study improves the understanding of O₃ formation mechanisms in a coastal industrial city during heat waves, and the elevated contributions of meteorological conditions to O₃ pollution become more challenge for the reduction of anthropogenic emissions controll.