[Impacts of Emission and Meteorological Conditions on Air Pollutants at Various Sites Around the COVID-19 Lockdown in Wuhan].

The random forest algorithm was used to separate the mass concentrations of six air pollutants (SO, NO, CO, PM, PM, and O) contributed by emissions and meteorological conditions. Their variations for five types of sites including Wuhan's central urban, suburb, industrial, the third ring road traffic, and urban background sites were investigated. The results showed that the values of PM/CO, PM/CO, and NO/CO during the lockdown period decreased by 10.8-21.7, 9.34-24.7, and 14.4-22.1 times compared with the period before the lockdown, indicating that the contributions of emissions to PM, PM, and NO were reduced. O/CO increased by 50.1-61.5 times, implying that the secondary formation increased obviously. The contributions of emissions to various types of pollutants all increased after the lockdown. During the lockdown period, affected by the operation of some uninterrupted industrial processes, PM concentrations in industrial areas dropped the least (20.5%). Compared with the lockdown period, residential activities, transportation, and industrial production were basically restored after the lockdown, resulting in the alleviation of the reduction in PM emission-related concentrations. The increase in emission-related O concentrations could be associated with the decreased NO and PM concentrations during the lockdown period. The elevated O partially offset the improved air quality brought by the reduced NOand PM concentrations. After the lockdown, (O) related with meteorology at the suburban and urban background sites increased by 16.2 μg·m and 16.1 μg·m, respectively, which could be attributed to the increased ambient temperature and decreased relative humidity. The decrease in PM and increase in O concentrations caused by reduced traffic and industrial emissions at the third ring road traffic and central urban regions can provide reference for the current coordinated and precise control of PM and O in subregions.