Enhanced ozone pollution in the summer of 2022 in China: The roles of meteorology and emission variations*

The variation of surface ozone (O3) is linked to changes in meteorology and emission. A record-breaking high temperature struck China in the summer of 2022, resulting in positive anomalies of daily maximum temperature of 0.86 +/- 1.02 degrees C. Consequently, the mean daily maximum 8 h average (MDA8) ozone (O3) increased by 6.46 +/- 13.0 mu g m- 3 compared to the mean summertime MDA8 O3 from 2014 to 2021 in China. This research aimed to understand the impact of meteorology and emission changes on O3 variations in different regions in the summer of 2022 by an explainable machine learning method. Results showed that the changes in emissions dominated the O3 enhancement in the Pearl River Delta (PRD), Beijing-Tianjin-Hebei (BTH), and Twain-Hu Basin (THB) with contributions of 89%, 86%, and 53% respectively. Satellite observations suggested that the increased O3 due to emission changes in BTH and PRD were related to the decreases in NO2 emissions and increases in volatile organic compound (VOC) emissions. On the contrary, variations in meteorology contributed 63%, 63%, and 51% respectively to the increases of O3 in the Sichuan Basin (SCB), Yangtze River Delta (YRD), and Fen-Wei Plain (FWP). The increase in O3 levels due to meteorological changes was associated with an anomalous westward extension of the Western Pacific Subtropical High during the summer of 2022. Specifically, the decrease in relative humidity, increases in temperature and boundary layer height were the dominant factors contributing to the increase of meteorology related O3 in SCB, THB, and YRD, with contributions over 99%. This study rec-ommends a continuous reduction in O3 precursor emissions to mitigate O3 pollution under the global warming background.