The impact of COVID-19-induced lockdowns during spring 2020 on nitrogen dioxide levels over major American counties

COVID-19 has quickly spread throughout the world, infecting and killing millions of people. In an effort to contain the spread of the virus, many governments implemented stringent lockdown measures. These lockdown restrictions, coupled with social distancing, severely curtailed transportation and industrial activities, which are the primary drivers of nitrogen oxides emissions. This study investigates whether lockdown orders in the United States have impacted tropospheric nitrogen dioxide (NO2) levels by evaluating 12 major counties with a total population of 38 million. For each county, Sentinel-5P satellite data were obtained and analyzed to determine NO2 column concentrations during the pre-lockdown, peak lockdown, and loosening lockdown periods in 2020. Then, NO2 levels were compared during these three periods to the same time frame in 2019. Our results show that the lockdowns in the 12 major U.S. counties analyzed led to a significant decline in NO2 levels, with an average reduction of 28.7% (±14.6%) and 17.6% (±10.9%) during peak lockdown and loosening lockdown periods, respectively.