Aggravated surface O₃ pollution primarily driven by meteorological variation in China during the early COVID-19 pandemic lockdown period

Abstract. Due to the lockdown during the COVID-19 pandemic in China from late January to early April in 2020, a significant reduction of primary air pollutants has been identified by satellite and ground observations. However, this reduction is in contrast with the increase of surface O₃ concentration in many parts of China during the same period. The reasons for this contrast are studied here from two perspectives: emission changes and inter-annual meteorological variations. Based on top-down constraints of NOx emissions from TROPOMI measurements and GEOS-Chem model simulations, our analysis reveals that NOx and volatile organic compound (VOC) emission reductions as well as meteorological variations lead to 8 %, -3 %, and 1 % changes in O₃ over North China, respectively. In South China, however, we find that meteorological variations cause ~30 % increases in O₃, which is much larger than -1 % and 2 % changes due to VOC and NOx emission reductions, respectively, and the overall O₃ increase is consistent with the surface observations. The higher temperature is the main reason that leads to the surface O₃ increase in South China. Overall, inter-annual meteorological variations have a larger impact than emission reductions on the aggravated surface O₃ pollution in China during the early lockdown period of COVID-19 pandemic.