Mobility, nightlights and air pollution during the early phases of the SARS-CoV-2 pandemic

The SARS-CoV-2 pandemic dramatically shifted daily life in the United States during 2020. The release of high spatial and temporal resolution cell phone data presented a unique opportunity to study the correlation between mobility, electricity use, and tropospheric NO₂. While many studies have identified trends of changes in air pollution in locations with reduced mobility due to Covid-19-related restrictions, these studies fall short of assessing whether these trends are statistically significant. Here we analyze if, and how much, mobility, nighttime light and NO₂ concentrations correlate. We analyze seven geographically diverse metropolitan areas in the United States (Atlanta, Austin, Boston, Denver, Los Angeles, New York City, Phoenix) in the first half of 2020. Using statistical tests of significance, we find that there is a strong correlation between NO₂ levels and nighttime light during February-July 2020 in all urban centers. Mobility and NO₂ are correlated strongly in four of the seven urban areas investigated. Together, these results suggest that policies aimed at limiting anthropogenic emissions from fixed (power generation) and mobile (traffic) NO₂ sources have an effect on air quality but additional factors should also be considered.