Diverse response of surface ozone to COVID-19 lockdown in China

Ozone (O(3)) is a key oxidant and pollutant in the lower atmosphere. Significant increases in surface O(3) have been reported in many cities during the COVID-19 lockdown. Here we conduct comprehensive observation and modeling analyses of surface O(3) across China for periods before and during the lockdown. We find that daytime O(3) decreased in the subtropical south, in contrast to increases in most other regions. Meteorological changes and emission reductions both contributed to the O(3) changes, with a larger impact from the former especially in central China. The plunge in nitrogen oxide (NO(x)) emission contributed to O(3) increases in populated regions, whereas the reduction in volatile organic compounds (VOC) contributed to O(3) decreases across the country. Due to a decreasing level of NO(x) saturation from north to south, the emission reduction in NO(x) (46%) and VOC (32%) contributed to net O(3) increases in north China; the opposite effects of NO(x) decrease (49%) and VOC decrease (24%) balanced out in central China, whereas the comparable decreases (45–55%) in these two precursors contributed to net O(3) declines in south China. Our study highlights the complex dependence of O(3) on its precursors and the importance of meteorology in the short-term O(3) variability.