Source: Geophysical Research Letters
Nitrogen dioxide (NO2) is a combustion pollutant that combines in the atmosphere to form particulate matter and ozone. It often serves as a surrogate for other forms of toxic pollution and can cause health problems in humans, especially those related to the respiratory system, like asthma. Most emissions come from cars, trucks, and other fossil fuel–burning equipment.
Although NO2 pollution can be harmful to all humans, U.S. neighborhoods with lower household incomes and in which residents are primarily people of color experience higher levels of air pollution than wealthier, whiter neighborhoods. This disparity has long been studied, but new tools are emerging to describe it more clearly.
In a new study, Demetillo et al. monitored NO2 across 52 major U.S. cities in neighborhoods with population densities greater than 1,000 people per square mile. The researchers measured near-daily NO2 concentrations using the satellite-mounted Tropospheric Monitoring Instrument, or TROPOMI, over cities representing 130 million residents. The instrument collects data at a finer spatial resolution than previously possible and allows for intracity comparisons across neighborhoods.
The results highlight air quality inequalities in cities across the country. NO2 concentrations are, on average, 12%–19% higher for communities of color than for white communities and 17% higher for people living below the poverty line. These inequalities are even higher in many individual cities. When race/ethnicity and income are factored in, whiter, more prosperous neighborhoods have an average of 28% less air pollution than their poorer, nonwhite neighbors. Phoenix, Los Angeles, and Newark, N.J., show the highest inequalities, with disparities of greater than 40%.
Comparing TROPOMI measurements on weekdays and weekends and on-the-ground emissions records, the authors show that diesel traffic like semitrucks, garbage trucks, and city buses are the primary emitters contributing to the inequalities. The research quantified the response of NO2 inequality to reductions in diesel emissions, finding that the 60% decline in diesel emissions on weekends causes a 40% decrease in disparities. In addition, the study found that the TROPOMI measurements clarified patterns in NO2 distribution across census tracts.
Although the results may help guide air pollution policy, they also point to the complexity of pollution inequality. The research determined that sustained diesel emissions controls will reduce—but not eliminate—pollution disparities across neighborhoods. The authors note that much work is still needed to address the respiratory diseases and reduced life expectancy linked to poor air quality. (Geophysical Research Letters, https://doi.org/10.1029/2021GL094333, 2021)
—Aaron Sidder, Science Writer