Nonuniform impacts of COVID-19 lockdown on air quality over the United States

Abstract

Most of the state governments in United States (U.S.) issued lockdown or business restrictions amid the COVID-19 pandemic in March 2020, which created a unique opportunity to evaluate the air quality response to reduced economic activities. Data acquired from 28 long-term air quality stations across the U.S. revealed widespread but nonuniform reductions of nitrogen dioxide (NO₂) and carbon monoxide (CO) during the first phase of lockdown (March 15-April 25, 2020) relative to a pre-lockdown reference period and historical baselines established in 2017-2019. The reductions, up to 49% for NO₂ and 37% for CO, are statistically significant at two thirds of the sites and tend to increase with local population density. Significant reductions of particulate matter (PM_2.5 and PM₁₀) only occurred in the Northeast and California/Nevada metropolises where NO₂ declined the most, while the changes in ozone (O₃) were mixed and relatively minor. These findings are consistent with lower transportation and utility demands that dominate NO₂ and CO emissions, especially in major urban areas, due to the lockdown. This study provides an insight into potential public health benefits with more aggressive air quality management, which should be factored into strategies to reopen the U.S. and global economy.

Keywords: Air pollution; COVID-19; Criteria air pollutants; NCore network; Urban-rural contrast.

Graphical abstract

Fig. 1

Change in ambient NO₂ concentration (ΔNO₂ %) due to the COVID-19 lockdown versus local population density based on a site's zip code. Site IDs are as noted in Table 1. Significant reductions are marked in green. The upper and lower dashed lines are visual guide for comparing the two OH and two MD sites, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)