Contributions of traffic and industrial emission reductions to the air quality improvement after the lockdown of Wuhan and neighboring cities due to COVID-19

Wuhan was locked down from January 23 rd to April 8 th , 2020 to prevent the spread of the novel coronavirus disease 2019 (COVID-19). Both the public and private transportations in Wuhan and its neighboring cities in Hubei Province were suspended or restricted, and the manufacturing industry was partially shut down. This study collected and investigated the ground monitoring data to prove that the lockdowns of the cities had significant influences on the air quality in Wuhan. The combined Weather Research and Forecasting Model (WRF) and Community Multiscale Air Quality Modeling System model (CMAQ) was used to evaluate the emission reduction from transportation and industry sectors and associated air quality impact. The results show that the emission from the transportation and industry sector reduced after the lockdown, while the emission from the industry sector reduced further after February 9 th . The reduction rate of pollutant concentration was 9.7%, 9.0%, 2.2%,18.4% and 13.4% from transportation, and was 48.5%, 50.0%, 63.8%, 65.6% and 40.8% from industry for PM2.5, PM10, SO2, NO2 and CO, respectively, compared to the ‘business as usual’ case during January and February in Wuhan. The industry shut down contributed significantly more to the pollutant reduction than the restricted transportation.