Substantial decreases in NO2 emissions from reduced transportation volumes in US cities during COVID-19 shutdowns reveal health vulnerabilities of urban populations

Abstract:

The air pollutant NO₂ is derived largely from transportation sources and is known to cause various respiratory diseases. Substantial reduction in transport and industrial processes around the globe stemming from the novel SARS-CoV-2 coronavirus and subsequent pandemic resulted in sharp declines in emissions, including for NO₂. Additionally, the COVID-19 disease that results from the coronavirus may present in its most severe form in those who have been exposed to high levels of air pollution and thus have various co-morbidities. To explore these links, we compared ground based NO₂ sensor data from 11 US cities from a two-month window from 2015-19 versus the same window during shutdown in 2020. Levels of NO₂ declined roughly 13-41% in 10 of the 11 cities in 2020, linked to similar declines in vehicle miles travelled (VMT) and traffic volume in some cities. To broaden the spatial analysis beyond the individual ground-based monitors, satellite data for tropospheric NO₂ was also analyzed, and was largely consistent with ground measurements. Many of the cities studied had a substantial percentage of the population with various pre-existing conditions, but a relationship was not found between NO₂ levels and respiratory disease, although a relationship was found between some cities and COVID-19 case counts. This finding indicates that VMT can be used as a tool in conjunction with ground-based sensors in examining and advocating for substantial improvements in air pollution and better policies perhaps leading to more population-level health resilience in the face of future pandemics.