Impacts of Certain Meteorological Factors on Atmospheric NO 2 Concentrations during COVID-19 Lockdown in 2020 in Wuhan, China

The concentration of nitrogen dioxide (NO 2 ) in the air is one of the important indexes for evaluating air quality. At the beginning of 2020, a COVID-19 outbreak suddenly hit Wuhan, China. To effectively control the epidemic, Wuhan was put under a 76-day lockdown, during which we collected tropospheric column amounts in the atmosphere and NO 2 concentrations measured at ground monitoring stations, and we reviewed the ground NO 2 concentrations in 2019 and the tropospheric NO 2 concentrations between 2012 and 2019. Using the random forest (RF) model, we predicted the impact of the tropospheric NO 2 concentration during the lockdown period without the occurrence of the COVID-19 epidemic and analyzed the impact of multiple certain meteorological factors on tropospheric and ground NO 2 concentrations. The results showed that the tropospheric and ground NO 2 concentrations were reduced by 11.04~53.36% and 21.96~65.04%, respectively. The main factors affecting the tropospheric NO 2 concentration were wind velocity, land surface temperature, surface lifted index, precipitable water volume and tropospheric relative humanity. The main factors affecting the ground NO 2 concentration were tropospheric relative humanity, surface lifted index, land surface temperature and tropospheric temperature. The development of different emission reduction and control measures under different meteorological conditions and the formulation of more refined policies will play positive roles in improving the efficiency of air pollution control.