COVID-19 Policy Impacts on NO2, Ozone, and PM2.5 Levels in U.S. Cities

Abstract:

The 2020 emergence of COVID-19 in the United States and resulting changes in activity due to policies and personal choices offer a unique opportunity to study the effect of anthropogenic emissions on air pollution levels. Previous research has identified decreases in nitrogen dioxide levels in many regions during the initial shutdowns, with smaller or negligible changes in ozone and fine particulate matter. However, there is limited research on changes in pollutant levels after stay-at-home orders ended. In particular, traffic volume and power plant emissions reflect the continuing shifts in human activity in response to policy updates. Quantifying fluctuations in human activity in conjunction with pollution levels enables us to better interpret the relationships between emissions and pollutant levels. Responses of pollutant levels to emissions are often nonlinear due to the complicated nature of atmospheric chemistry, especially for the formation of ozone and secondary particulate matter from precursor emissions. Consequently, examining air quality changes together with changes in human activity can offer insight into the potential impacts of policies that influence emissions.

In our study, we use publicly available NO₂, ozone, and PM_2.5 data from regulatory monitors to quantify the trends in these pollutants in major metropolitan regions of the United States. We find, in certain locations, notable differences in pollution amounts in 2020 compared to historical data, focusing on a 2017 to 2019 baseline. Furthermore, we correlate changes in air pollution in each region with changes in traffic levels and power plant emissions, considering periods before, during, and after COVID-19 stay-at-home periods. We examine the consistency of temporal and spatial patterns in changes in human activity and air pollutant levels within and across the regions.