The impact of COVID-19 on urban PM2.5 -taking Hubei Province as an example*

In January 2020, China implemented strict lockdown measures due to the invasion of the new coronavirus, which led to a sharp decline in the contribution of anthropogenic fine particulate matter (PM2.5). The special period of COVID-19, especially in Hubei where the epidemic was the most severe, provides excellent research conditions for studying the contribution of anthropogenic activities to PM2.5 concentrations. We used an optimized deep learning model to predict PM2.5 concentration during the epidemic period in the cities of Hubei Province. The contributions of local anthropogenic activities to PM2.5 pollution were obtained by contrasting the predicted results with actual site observations. However, a strange phenomenon was revealed that Yichang, a city with low local anthropogenic contribution to PM2.5, was found to have severe haze in winter conflicting with our previous expectations. After further research, we found that an increased conversion of secondary aerosols caused by long-distance transport of pollutant gases from the northern region is the main cause of winter haze pollution in this city. This finding highlights the importance of joint regional prevention and control of air pollution.