Not all air is created equal.

While air quality has improved across the United States in recent decades, significant disparities persist in terms of who breathes the worst air. Communities exposed to the most air pollution in the 1980s — often poor and with high proportions of Black and Hispanic residents — are largely in the same position today, researchers report in the July 31 Science.

Lots of different pollutants can clog the air, but scientists are especially interested in particulate matter less than 2.5 microns in diameter. Called PM2.5, the tiny particles are associated with myriad health problems, including cardiovascular disease, respiratory illness, diabetes and neurological problems (SN: 9/19/17).

Marginalized communities, often closer to factories or major roadways than whiter, wealthier communities, bear the brunt of PM2.5 pollution. That exposure contributes to stark racial health inequities in the United States. “There hasn’t been clear documentation of how these disparities have evolved over time,” says Jonathan Colmer, an economist at the University of Virginia in Charlottesville. The U.S. Environmental Protection Agency only began measuring PM2.5 in 1999. Addressing current inequities requires an understanding of the past, Colmer says.

He and colleagues estimated annual average PM2.5 levels for each square kilometer in the country from 1981 to 2016 using published data derived from satellites and simulations of pollutant movement through space. The team then mapped those estimates onto about 65,000 census tracts to rank neighborhoods from most to least polluted annually, and noted how rankings changed over time.

Whereas average PM2.5 concentrations decreased by 70 percent across the entire country, the relative ranking of neighborhoods hardly budged.

On average, whiter, more affluent neighborhoods were less polluted throughout the 36-year time frame. Disadvantaged neighborhoods with more Black or Hispanic people remained more polluted, despite experiencing a larger absolute drop in PM2.5 levels.

“It’s really good news that air pollution is dropping for everyone,” says Anjum Hajat, an epidemiologist at the University of Washington in Seattle who wasn’t involved in the research. But even relatively low levels of pollution pose significant health risks, and the reductions might not translate to improved health for the hardest-hit communities. “To me, the take-home message is that inequity is very stubborn.”

The study wasn’t designed to address why these inequities persist, though a move away from manufacturing or coal production was associated with air quality improvements in certain neighborhoods.

More important, Hajat says, is power structure. “The communities that were the most marginalized and had the least political power in the 1980s are likely the same communities that continue to have the least power today.”

White, wealthy communities have been able to prevent polluting facilities from being placed in their communities, she says, while marginalized communities often haven’t had this power. To see real change, “marginalized communities need to be included in discussions about their future,” she says, for instance through community members holding decision-making roles.