The Impact Of COVID-19 On Urban PM_2.5 ——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(PM_2.5).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 PM_2.5concentrations.In order to explore the impact of the blockade policy during the COVID-19 period on the concentration of air pollutants in Hubei,and further reveal the contribution of human activities to the concentration of PM_2.5.This study collected data from state-controlled air quality stations in 13 major cities in Hubei Province.Selecting MODIS AOD data,meteorological data from the European Centre for Medium-Range Weather Forecasts,etc.as input parameters,an optimized deep learning model was constructed to predict PM_2.5concentrations during the COVID-19 lockdown period in cities in Hubei Province.The contributions of local anthropogenic activities to PM_2.5pollution were obtained by contrasting the predicted results with actual site observations.Research findings show that the improved hybrid prediction model,Gauss-LSTM＆BP,has a very good performance in predicting PM_2.5concentration（CV-RMSE=8.31,CV-R~2=0.80）.During the lockdown period,the most severely affected area,Wuhan,had a decrease of 26.38%percent（17.3μg/m~3）and the concentration in Hubei Province decreased by 22.61%percent（14.4μg/m~3）on average.Compared with Hubei Province,Wuhan has reduced more absolute values and percentages.This may be due to the fact that Wuhan is the central city of Hubei Province and Wuhan has adopted stricter lockdown measures.The impact of COVID-19 on the concentration of PM_2.5in Hubei Province is characterized by high values in the east and low values in the west.However,a strange phenomenon emerged:Yichang is the second largest city in Hubei Province by industrial output value.Severe smog is observed every winter,but a low local anthropogenic contribution to PM_2.5was found in the city,contradicting our previous expectations.After further research,we found that an increased conversion of secondary aerosols caused by long-distance air mass 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.China has a large land area and diverse landforms.Pollution prevention and control must use complex systems engineering thinking.Our research provides a reference for the implementation of the government’s precise and quantitative air pollution control policy,and provides ideas and methods for our next larger-scale（China or world）research.