To better understand the most affected populations, Camilleri, Horton and their co-investigators turned to a nationwide land use regression model (LURM) to estimate NO2 concentrations. The LURM incorporates surface NO2 observations and remotely sensed satellite observations along with land use and roadway information to predict the concentration of NO2 pollution.
“Land use regression models estimate pollutant concentrations by associating land use with observed pollutant concentrations,” Horton said. “We know that a roadway has higher NO2 than a park, for example. Surface observations help inform that relationship, and satellite data can further constrain it. These associations allow us to estimate NO2 concentrations across the contiguous United States.”
Profound impact on Black communities
By combining land use, monitor and satellite data, the researchers estimated NO2 concentrations across areas as small as one kilometer throughout the contiguous United States. Then, to characterize the residents living within these areas, the researchers used population and demographic data from the American Community Survey and mortality rates at the census-tract level derived by Industrial Economics, Inc.
47%
In predominantly Black census tracts, premature deaths related to NO2 exposure are 47% higher than the national average
At a national level, the researchers found areas with the largest estimated NO2-attributable mortality rates are 29% Black, 18% Hispanic or Latinx, 5% Asian and 45% white. Considering that the racial and ethnic makeup of total U.S. population is 12% Black, 18% Hispanic or Latinx, 5% Asian and 61% white, the disproportionate impact on Black communities is profound.
Nationwide urban hotspots
Because internal combustion engine-based transportation is one of the greatest sources of NO2 emissions, peak concentrations of the pollutant accumulate along highways and major road networks. A large portion of people living close to these hotspots are people of color, who generally have higher-than-average susceptibilities, the authors write.
Filled with dense highways and industrial activity, urban areas experience the highest rates of NO2-related deaths. The larger Detroit area in Michigan, specifically, experiences the highest premature death rate in the country with 1.6 times more NO2-attributable mortalities than the U.S. average. The researchers uncovered a similar pattern in the Chicago and New York City metropolitan areas, where mortality rates are 1.3 and 1.4 times higher than the national average.
The disproportionate burden on marginalized communities is amplified in these areas. For example, Black people make up just 21% of the population in the larger Chicago and Detroit metropolitan areas, yet about 60% of the people affected by NO2-related mortality in these areas are Black.
Exploring potential solutions
To address the unjust impacts of NO2 pollution, Camilleri and Horton suggest the adoption of policies that incentivize vehicle electrification and the removal of high-emitting combustion-engine vehicles from roadways. Just last month, their team published a study finding that electrifying 30% of on-road heavy-duty vehicles could save hundreds of lives per year — largely benefitting disadvantaged communities.
“Based on our previous work, we have shown that shifting to cleaner transportation options can have large implications for reducing inequitable transportation-related health burdens,” Camilleri said. “The shift to electric vehicles is definitely one solution that is worth incentivizing from an air quality, public health, climate change and economic perspective.”
The study, “All-cause NO2-attributable mortality burden and associated racial and ethnic disparities in the U.S.,” was a collaborative effort among Northwestern and George Washington University researchers and was supported by the National Science Foundation and NASA.