An analysis of nearly 2 years of satellite data from major US cities shows widespread inequality in exposure to the air pollutant nitrogen dioxide from neighborhood to neighborhood. On average, people with incomes at or below the poverty line and who are members of marginalized racial and ethnic groups are exposed to about 28% higher concentrations of NO2 than higher-income White people living in the same city, the study finds. And it ties this inequity to heavy-duty diesel trucking (Geophys. Res. Lett. 2021, DOI: 10.1029/2021GL094333).
Nitrogen dioxide irritates the respiratory system. It also reacts to form ozone and particulate matter, both of which have adverse health effects.
Last year, University of Virginia atmospheric chemist Sally Pusede and PhD student Mary Angelique Demetillo used data from a NASA flight campaign to validate the use of satellite measurements to examine variations in NO2 concentrations within a city. They demonstrated that daily measurements of NO2 made by the TROPOMI satellite could be used to illuminate air pollution inequality among census tracts in Houston (Environ. Sci. Technol. 2020, DOI: 10.1021/acs.est.0c01864).
In their new work, Pusede and Demetillo expanded their study to 52 major US cities where about 130 million people live. They saw inequality in every city, but cities with worse air quality also had more NO2 inequality. In Phoenix, people living in poverty who are part of marginalized racial and ethnic groups experience levels of NO2 46% higher than White people with incomes above the poverty line. The numbers are similar in Los Angeles, and in Newark, New Jersey.
As for the origin of that pollution, “We find that diesel trucking is the largest source of NO2 inequality” in all cities in the study, Pusede says. Pusede and her team focused in on the effect of NO2 emissions from heavy duty diesel traffic by comparing NO2 emissions on weekdays and weekends, when most heavy duty diesel trucks are off the road. Across the cities in the study, a 62% reduction in diesel traffic on weekends reduced the exposure of marginalized groups to NO2 so much that inequality decreased by 37%.
The rest of the inequality is driven by gasoline vehicles, construction equipment, and stationary sources such as power plants, Pusede and Demetillo find.
Gaige Kerr, a postdoctoral researcher at George Washington University, says this work is an important addition to a growing body of evidence of the underlying sources of NO2 inequality. His recent work shows that NO2 exposure disparities persisted during the COVID-19 lockdowns. Kerr says it’s time to rethink how goods are moved around the country by rerouting diesel traffic and electrifying the heavy duty trucking industry.