Denver communities of color bear the brunt of city's air pollution: Study

Communities of color in the Denver metropolitan area are exposed to higher levels of air pollution than non-Hispanic white residents, a new study has found.

The disparity in environmental conditions is due to historic tendencies for these populations to reside in both historically redlined neighbors and near highways, according to the study, published on Wednesday in Environmental Science and Technology.

The communities experiencing the most adverse impacts are residents of Hispanic/Latino and American Indian and Alaska Native heritage, the research determined.

“We just focused on Denver and redlining practices that took place in the 1930s and 1940s,” the study's lead author Alex Bradley, a chemistry graduate student at the University of Colorado Boulder, said in a statement.

“Every city has a story of why people live where they do, and that affects who is affected most by pollution," Bradley added.

The practice of "redlining" stems from a New Deal era policy that led to the establishment of several government programs aimed at broadening homeownership through mortgages and loans, the authors noted.

As part of these programs, however, neighborhoods with primarily Black or immigrant populations often received a "hazardous" rating for repayment — leading to the redlining practice that limits lending.

These discriminatory policies became common when entities such as the Federal Housing Administration and the Home Owner's Loan Corporation started assigning the ratings in question. To do so, they ranked neighborhoods from "A," the least risky, to "D," the riskiest areas that were color-coded in red.

Although research has increasingly shown that historically redlined areas endure higher levels of air pollution than those that received better ratings, the University of Colorado team aimed to explore the roots of these differences in Denver.

“Denver has some known, large sources of air pollution that are outside the city boundaries, like agriculture, oil and gas production, and wildfires,” corresponding author Joost de Gouw, a CU Boulder professor of chemistry, said in a statement.

“Going into the study one could have expected that people in Denver are exposed more evenly to air pollution. But that is not what we found," de Gouw added. 

The researchers focused on the presence of two pollutants: nitrogen dioxide (NO2), which comes from vehicles and power generation, and PM 2.5, fine particulate matter that stems from vehicle exhaust, cooking and wildfires.

NO2 is a recognized source of ozone pollution in the summer in the Denver region, while particulate matter is more problematic in the winter, the authors noted.

To measure pollution levels across the city, the researchers used satellite images and other satellite-based models, while combining the data with historical redline maps.

The researchers found that districts graded D in 1939 had higher air pollution than districts graded A — with the former showing about 13 percent greater NO2 levels than the latter.

After identifying the differences in pollution levels, the authors used 2020 census tracts to identify a correlation between pollution levels and race. Ultimately, they determined that non-Hispanic white and Asian/Asian-American populations in Denver enjoy far better air quality than Hispanic/Latino, American Indian and Alaska Native communities.

The researchers then applied their method to 200 other U.S. cities that had practiced redlining and saw similar impacts.

While the effects may share commonalities, the reasons behind the environmental pollution discrepancies in different cities mandate their own historical analysis, the authors explained.

For example, the settlement patterns of Hispanic and Latino populations in Denver were driven largely by a sugar beet boom in the early 20th century and a surge in manufacturing jobs during World War II, according to the study.  

Although on a national level, redlining is generally considered to have most affected Black and African American communities, the researchers found that only three of the 16 districts graded "D" in Denver met this description.

More spread out during this era were Eastern European immigrants and Italians, as well as Mexican and New Mexican agricultural workers and some Japanese vegetable farmers, the authors noted.

Denver's Black and African American communities, on the other hand, were "compressed into too-small neighborhoods" via exclusionary zoning policies that pre-date redlining, per the study.

Expanding their search beyond initial redlining policies, the authors also looked into how transportation infrastructure has contributed to these disparities.

Harnessing data from the National Oceanic and Atmospheric Administration to track fuel emissions, they zoomed in on the multiple Denver highways built through redlined districts in the 1960s.

Gas and diesel emissions from traffic were greater in census tracks that largely included people of color, who tended to live in closer proximity to major highways, according to the study.

"It still matters where you live and how close you are to industrial sources and highways inside the city boundaries," de Gouw said.

Bradley, meanwhile, expressed hopes that this comprehensive look at Denver's air quality patterns could help provide tools for change.

"People living in these communities will not be surprised by our data," he added.