RESUMO
In recent yearsï¼ regional compound air pollution events caused by fine particles ï¼PM2.5ï¼ and ozone ï¼O3ï¼ have occurred frequently in economically developed areas of Chinaï¼ in which atmospheric oxidizing capacity ï¼AOCï¼ has played an important role. In this studyï¼ the WRF-CMAQ model was used to study the impacts of anthropogenic emission reduction on AOC during the COVID-19 lockdown period. Three representative cities in eastern China ï¼Shijiazhuangï¼ Nanjingï¼ and Guangzhouï¼ were selected for an in-depth analysis to quantify the contribution of meteorology and emissions to the changes in AOC and oxidants and to discuss the impact of AOC changes on the formation of secondary pollutants. The results showed thatï¼ compared with that in the same period in 2019ï¼ the urban average AOC in Shijiazhuangï¼ Nanjingï¼ and Guangzhou in 2020 increased by 60%ï¼ 48.7%ï¼ and 12.6%ï¼ respectively. The concentrations of O3ï¼ hydroxyl radical ï¼·OHï¼ï¼ and nitrogen trioxide ï¼NO3·ï¼ increased by 1.6%-26.4%ï¼ 14.8%-73.3%ï¼ and 37.9%-180%ï¼ respectively. The AOC in the three cities increased by 0.06×10-4ï¼ 0.12×10-4ï¼ and 0.33×10-4 min-1ï¼ respectivelyï¼ due to emission reduction. The meteorological change increased AOC in Shijiazhuang and Nanjing by 20% and 17.9%ï¼ respectivelyï¼ but decreased AOC in Guangzhou by -9.3%. Enhanced AOC led to an increase in the nitrogen oxidation ratio ï¼NORï¼ and VOCs oxidation ratio ï¼VORï¼ and promoted the transformation of primary pollutants to secondary pollutants. This offset the effects of primary emission reduction and resulted in a nonlinear decline in secondary pollutants compared to emissions during the COVID-19 lockdown.