Sensitivity of O3 formation from anthropogenic precursor emissions in typical cities in the Chengdu-Chongqing region: A simulation study

Cao, Y.; Li, Z.; Pu, X.; Jiang, C.; Xue, W.; Jiang, H.; Zhang, W.; Zhai, C.

The study focuses on the emerging events of ozone formation in Chengdu-Chongqing areas, southwestern China in March-April 2019, investigating the sensitivities of ozone (O3) formation from anthropogenic precursor emissions in the Chengdu-Chongqing region. The study used the CAMx-DDM air quality model by changing scenarios of pollutants emissions due to the prevention and control measures of the "COVID-19" pandemic in 2020. The simulation results show the negative sensitivity of O3 to NOx and the positive sensitivity to VOCs in Chengdu-Chongqing area. The higher sensitivity areas include the main urban area of Chongqing, the west of the main urban area, the southern urban agglomeration of Sichuan and the western part of Chengdu plain, due to their intensive distributions of pollution emission sources. For example, the average sensitivity of O3 hourly concentration to NOx and VOCs from March to April in 2019 is -19.14 μg•m-3and 7.25 μg•m-3 respectively in the main urban area of Chongqing. The result shows opposite diurnal variations because of the emissions from local and surrounding areas. The simulation results showed that under the condition of 25% reduction of VOCs emissions in these regions, the monthly mean ozone maximum 8-hour concentration in March and April decreased by 2.62 μg•m-3 and 3.59 μg•m-3, respectively. Sensitivity simulation results show that in March 2020, NOx emissions in Sichuan Province and Chongqing decreased by 8.00% and 22.40%, VOCs decreased by 1. 00% and 7.92%. In April, NOx emissions increased by 5.00% and 9.50% year on year, VOCs in Sichuan province were flat year on year, and VOCs in Chongqing increased by 3.63%, which was very consistent with the actual emissions caused by the prevention and control of the "COVID-19" epidemic and the recovery of production in the same period. © 2021, Science Press. All right reserved.