Substantial Decreases in U.S. Cities’ Ground-Based NO 2 Concentrations during COVID-19 from Reduced Transportation

A substantial reduction in global transport and industrial processes stemming from the novel SARS-CoV-2 coronavirus and subsequent pandemic resulted in sharp declines in emissions, including for NO 2 . This has implications for human health, given the role that this gas plays in pulmonary disease and the findings that past exposure to air pollutants has been linked to the most adverse outcomes from COVID-19 disease, likely via various co-morbidities. To explore how much COVID-19 shutdown policies impacted urban air quality, we examined ground-based NO 2 sensor data from 11 U.S. cities from a two-month window (March–April) during shutdown in 2020, controlling for natural seasonal variability by using average changes in NO 2 over the previous five years for these cities. Levels of NO 2 and VMT reduction in March and April compared to January 2020 ranged between 11–65% and 11–89%, consistent with a sharp drop in vehicular traffic from shutdown-related travel restrictions. To explore this link closely, we gathered detailed traffic count data in one city—Indianapolis, Indiana—and found a strong correlation (0.90) between traffic counts/classification and vehicle miles travelled, a moderate correlation (0.54) between NO 2 and traffic related data, and an average reduction of 1.11 ppb of NO 2 linked to vehicular data. This finding indicates that targeted reduction in pollutants like NO 2 can be made by manipulating traffic patterns, thus potentially leading to more population-level health resilience in the future.