NASA scientists and others using
data from NASA and our partner satellites have shown that air pollution levels dropped significantly during COVID-19. A new, NASA-funded study, conducted by scientists at The George Washington University (GW) in Washington, D.C., zoomed in on the 15 largest metropolitan areas in the United States to see
how the drop in air pollution differed from neighborhood to neighborhood. The paper was published July 20 in the journal Proceedings of the National Academy of Sciences.
We talked to the lead author on the study, Gaige Kerr, about how the COVID-19 pandemic led to better air quality – and how those improvements were unequal for people of different races, ethnicities and socioeconomic levels. Kerr is a research scientist at GW. The interview has been lightly edited for clarity.
What is nitrogen dioxide and how is it related to air quality?
Nitrogen dioxide, or NO2, is a trace gas in the atmosphere. It’s one of the six air pollutants regulated by the
U.S. Environmental Protection Agency (EPA) under the
Clean Air Act. Even though NO2 is only present in small amounts, it’s very harmful for human health and can trigger respiratory illnesses like asthma. NO2 also leads to the formation of ozone near Earth’s surface, another harmful air pollutant.
NO2 can come from natural things like lightning or microbes in the soil. But in cities, the majority of NO2 stems from human activity and fossil fuel combustion. Roughly 50% of the ambient NO2 comes from traffic emissions. The other large sources come from power plants, incinerators and factories.
What happened with NO2 levels when the COVID-19 pandemic triggered lockdowns in March 2020?
During COVID, we had the opportunity to see how taking many cars off of the road and planes out of the skies affected air pollution in the real world in this unintended experiment. We know from past research that there are NO2 pollution disparities based on several factors – most notably race, ethnicity and income – and that communities of color and lower socioeconomic status face much higher concentrations of NO2. So, we wanted to understand how this unprecedented, extraordinary drop in human activity and emissions impacted NO2 disparities.
In cities, NO2 levels plummeted at first. That had a lot to do with the drop in traffic and travel, since vehicle traffic is the largest contributor to NO2 in cities. We saw widespread decreases in NO2 across urban areas in the United States during the pandemic, but the magnitude varied. NO2 levels dropped by about 10% to 35% on average, depending on the city. New York City and Los Angeles had very large drops, but NO2 disparities across different racial, ethnic and socioeconomic groups were very large in these cities.