Urban meteorology–chemistry coupling in compound heat–ozone extremes

Abstract

Heatwaves and ozone (O3) pollution threaten human and ecosystem health, with their compounding effects particularly severe in cities. While ground-based observations are indicative of urban O3 pollution during heatwaves, limited vertical insights into the intensified and prolonged O3 pollution hinder a comprehensive understanding of the underlying mechanisms and mitigation strategies. Here, leveraging airship vertical measurements and meteorology–chemistry coupled modeling, we reveal that heatwave-reinforced turbulence redistributes precursors vertically, altering photochemical stratification and accelerating O3 production both at the surface and aloft over megacities in China. Stringent emission controls targeting nitrogen oxides could mitigate the heatwave-exacerbated O3 extremes by narrowing the vertical disparity of photochemical sensitivity. Although heatwaves are projected to intensify, emission reductions due to China’s carbon neutrality pledge could alleviate urban O3 pollution by 41–47% during heatwaves and help tackle the dual challenges of air pollution and global warming while enhancing the climate resilience of city clusters. Heatwaves and ozone pollution pose compounded risks to urban health, but limited vertical insights have hindered understanding of their interaction. Using airship observations and model simulations, this study reveals that heatwaves worsen urban ozone pollution by vertically redistributing precursors, while emission reductions could mitigate heat–ozone extremes in a warming climate.