| Based on the pollution emission survey and the observation data of air quality and component stations, the WRF/SMOKE/CMAQ model system was adopted to analyze the impact of pollution sources and changes in meteorological conditions on air quality during the COVID-19 outbreak. The results showed that during the COVID-19 outbreak in 2020, in addition to the year-on-year increase in ρ(O3) in the Sichuan Basin, ρ(SO2), ρ(NO2), ρ(CO), ρ(PM2.5), and ρ(PM10) all decreased year-on-year, with decreases ranging from 8% to 41%. Compared with levels from the same period in 2019, ρ(Cl-), ρ(K+), ρ(Si), ρ(Al), ρ(Ca), and ρ(EC) in Chengdu decreased year-on-year, indicating that the emission reduction of construction sites, motor vehicles, industrial coal burned, and biomass combustion were the main reasons for the decrease in PM2.5 concentration. During the COVID-19 outbreak, the SO2, NOx, PM10, PM2.5, and VOCs industrial emissions decreased by 32%, 31%, 40%, 39%, and 41%, respectively. The traffic volume of motor vehicles in Chengdu was only 40.3% of that during the normal period, and the speed of traffic increased by 19.7%. The daily emissions of NOx, VOCs, and CO were reduced by 44.7%, 49.6%, and 38.0%, respectively. The non-equal decrease in pollutants made the atmospheric oxidability contributed by motor vehicle emissions relatively further enhanced. The unfavorable weather conditions in the Sichuan Basin caused ρ(PM2.5), ρ(NO2), ρ(SO2), ρ(O3), and ρ(PM10) to rise by 2%, 4%, 23%, 6%, and 8%, respectively. After deducting the influence of changes in weather conditions, the concentrations of ρ(PM2.5), ρ(NO2), ρ(SO2), and PM10 decreased by 21%, 45%, 31%, and 30%, respectively, and ρ(O3) increased by 12%. |
