Quantifying anomalies of air pollutants in 9 U.S. cities during 2020 due to COVID-19 lockdowns and wildfires based on decadal trends

Abstract

The COVID-19 pandemic led many state and local governments in the United States to enact lockdowns to control the spread of the virus. These actions led to lower on-road emissions as a significant portion of the workforce began working from home. Here, we examine the concentrations of primary pollutants, nitrogen dioxide (NO2) and carbon monoxide (CO), a secondary pollutant, ozone (O3), and one that is both a primary and secondary pollutant, particulate matter (PM2.5), from 9 U.S. cities in 2020 using data reported to the U.S. Environmental Protection Agency to determine how they changed during the pandemic. We used a multiple linear regression model fitted to historical data to account for meteorology and found concentrations of NO2, O3, and CO generally decreased in the 9 cities in late March and early April, consistent with previous literature and a fuel-based emissions inventory. We further found the decadal trends of the 4 pollutants were decreased in the summer months for most of the cities studied. An analysis of weekend decreases in NO2 was consistent with previous studies; however, the weekend increases in O3 were typically dominated by reduced NOx titration. We further detect anomalous increases in NO2, CO, O3, and PM2.5 in western U.S. cities in the late summer, which we attribute to wildfire emissions. Finally, we examined diel profiles to determine when changes due to COVID-19 lockdowns and late-summer wildfires were most apparent during the day.