Restrictions on human activities remarkably reduced emissions of air pollutants in China during the COVID-19 lockdown periods. However, distinct responses of O₃ concentrations were observed across China. In the Beijing–Tianjin–Hebei (BTH) and Yangtze River Delta (YRD) regions, O₃ concentrations were enhanced by 90.21 and 71.79% from pre-lockdown to lockdown periods in 2020, significantly greater than the equivalent concentrations for the same periods over 2015–2019 (69.99 and 43.62%, p < 0.001). In contrast, a decline was detected (−1.1%) in the Pearl River Delta (PRD) region. To better understand the underlying causes for these inconsistent responses across China, we adopted the least absolute shrinkage and selection operator (Lasso) and ordinary linear squares (OLS) methods in this study. Statistical analysis indicated that a sharp decline in nitrogen dioxide (NO₂) was the major driver of enhanced O₃ in the BTH region as it is a NO_x-saturated region. In the YRD region, season-shift induced changes in the temperature/shortwave radiative flux, while lockdown induced declines in NO₂, attributable to the rise in O₃. In the PRD region, the slight drop in O₃ is attributed to the decreased intensity of radiation. The distinct regimes of the O₃ response to the COVID-19 lockdown in China offer important insights into different O₃ control strategies across China.

Climate change may aggravate air pollution through evolving meteorological conditions. We use observations and reanalysis to explore how meteorological persistence affects extremes of summertime O3 and wintertime PM2.5 pollution in China, and changes in the distributions at the high end are discussed with contrasting conditions of climate. Median summertime O3 significantly increase as air stagnation days sustains, with 0.15, 0.15 and 0.10 standard deviation per day in the Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions. Negligible variations of summertime O3 are found during continuous high temperature days, although BTH and YRD regions witness highest probability of a high O3 day on the 4th day of 4 consecutive high temperature days. In contract, successive stagnation days result in enhanced 90th percentile PM2.5 concentration, instead of median. Analysis on inter-monthly timescale demonstrate that tail of O3 concentrations in megacities are amplified in relation to mean daily maximum T and co-occurrences of high T & stagnation, while significant enhancement of tail with stagnation is found for wintertime PM2.5. These results suggest that megacities with relatively high emissions are more vulnerable to a hotter and more stable future.