Racial Disparities in Air Pollution Where Most Americans Live Worse Than Previously Understood

July 7, 2022

An analysis of racial disparities in urban air pollution reveals starker differences than previously understood in the communities where most Americans live. Compared to earlier studies, researchers found more substantial increases in concentrations of fine particulate matter (PM2.5) comparing census tracts with no Black residents with census tracts with a small percent of Black residents. The findings are published in the journal Environmental Health Perspectives.

Scientists at Columbia University Mailman School of Public Health and partners modeled census tract level PM2.5 concentrations using a nonlinear method that accounts for poverty and population density using data from 2010. The nonlinear method allows for the relationship between race/ethnicity and air pollution to change across communities.

“Much research has documented racial disparities but in communities at the tail of the distribution, such as where a community is 80 percent Black. We see this disparity begin when just a few Black individuals enter a community, meaning we see an immediate disparity in communities where most Americans live,” says senior author Joan Casey, PhD, assistant professor of environmental health sciences at Columbia Mailman School.

The researchers found that the standard linear method underestimated the severity of air pollution in areas with low percentages of Black residents. Using the new nonlinear method, the difference in PM2.5 concentrations between an area without any Black residents and 10 percent Black residents is +1.1 µg/m3 of PM2.5 versus a difference of +0.09 µg/m3 in the linear model. The linear method also seems to overestimate the severity of air pollution in areas with high percentages of white residents. Using the nonlinear method, the difference in air pollution concentrations between an area with 80 percent vs. 90 percent white is -0.47 µg/m3 of PM2.5 vs. -0.17 µg/m3 in the linear model.

These differences are important because even a 1 µg/m3 increase in PM2.5 can increase risk of numerous health outcomes including adverse birth outcomes and cardiovascular disease. The larger than previously recognized disparities in air pollution where most Americans live may have implications for persistent racial health disparities in the United States.

The researchers’ use of this method was informed by their understanding of how historical sociopolitical processes differently impacted neighborhoods with small vs. large non-white populations.

First author Misbath Daouda, a PhD candidate in environmental health sciences at Columbia Mailman School of Public Health, says: “History shows that even a relatively small Black population can set-off racist practices that restrict where these individuals can live and work, which can lead to additional exposure to environmental hazards like air pollution. For instance, a slight relative increase of the Black population in Birmingham, Alabama, in the early 1900s led to the implementation of a racially restrictive zoning ordinance in 1926, which resulted in the least desirable and most hazard-prone land in the city being zoned for Black residence. In 2010, Black Americans were about twice as likely to live in areas where PM2.5 concentrations exceeded the 90th percentile nationwide than white and Hispanic Americans.”

Co-authors include Lucas Henneman, George Mason University, Fairfax, Virginia; and Jeff Goldsmith and Marianthi-Anna Kioumourtzoglou at Columbia Mailman School.