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The outbreak of 2019 novel coronavirus has hugely impacted the world and becomes a global public threat. To prevent the spread of COVID-19, human activities are largely restricted in China in early February, 2020. The influence of strict COVID-19 control policies on air quality and the potential influence of particulate matter concentration on COVID-19 infection in China are of great interest. This study analyzes the concentrations of six major air pollutants in 366 urban areas across mainland China during January 1 to April 30 in 2017-2020. Results show that strict COVID-19 control policies have significantly improved the air quality in many provinces. Compared to 2019, national mean concentrations of PM 2.5 , PM 10 , SO 2 , NO 2 and CO in 2020 decrease by 14%, 15%, 12%, 16% and 12%, respectively, while the concentration of O 3 increases by 9%. Generally, the diurnal variation of PM 2.5 and PM 10 concentrations remains unchanged during COVID-19 and their concentrations are high in the morning and evening while low in the afternoon. Correlation analysis shows that daily COVID-19 infections are positively correlated with PM 2.5 concentration in many provinces, indicating a potential risk of aerosol transmission in high PM 2.5 environment. Thus it is suggested to stay at home in highly polluted days and go out in the afternoon to reduce the risk of infection due to aerosol transmission.

The outbreak of 2019 novel coronavirus (COVID-19) has hugely impacted the world and becomes a global public threat. To prevent the spread of COVID-19, human activities are largely restricted in China in early February, 2020. The influence of strict COVID-19 control policies on air quality and the potential influence of particulate matter concentration on COVID-19 infection in China are of great interest. This study analyzes the concentrations of six major air pollutants in 366 urban areas across mainland China during January 1 to April 30 in 2017-2020. Results show that strict COVID-19 control policies have significantly improved the air quality in many provinces. Compared to 2019, national mean concentrations of PM 2.5 , PM 10 , SO 2 , NO 2 and CO in 2020 decrease by 14%, 15%, 12%, 16% and 12%, respectively, while the concentration of O 3 increases by 9%. Generally, the diurnal variation of PM 2.5 and PM 10 concentrations remains unchanged during COVID-19 and their concentrations are high in the morning and evening while low in the afternoon. Correlation analysis shows that daily COVID-19 infections are positively correlated with PM 2.5 concentration in many provinces, indicating a potential risk of aerosol transmission in high PM 2.5 environment. Thus it is suggested to stay at home in highly polluted days and go out in the afternoon to reduce the risk of infection due to aerosol transmission.