Changes in U.S. air pollution during the COVID-19 pandemic

The COVID-19 global pandemic has likely affected air quality due to extreme changes in human behavior. We assessed air quality during the COVID-19 pandemic for fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) in the continental United States from January 8th-April 21st in 2017-2020. We considered pollution during the COVID-19 period (March 13-April 21st) and the pre-COVID-19 period (January 8th-March 12th) with 2020 representing 'current' data and 2017-2019 representing 'historical' data. County-level pollution concentrations were compared between historical versus current periods, and counties were stratified by institution of early or late non-essential business closures. Statistically significant NO₂ declines were observed during the current COVID-19 period compared to historical data: a 25.5% reduction with absolute decrease of 4.8 ppb. PM_2.5 also showed decreases during the COVID-19 period, and the reduction is statistically significant in urban counties and counties from states instituting early non-essential business closures. Understanding how air pollution is affected during COVID-19 pandemic will provide important clues regarding health effects and control of emissions. Further investigation is warranted to link this finding with health implications.