The Clean Air Act works, but not equally

The US Clean Air Act (CAA) has improved air quality, but not equally for all people. According to a new study, while pollutant emissions have decreased over time, how much they have fallen in a given area depends on the demographics of people living there and the sources and types of the pollution (Nat. Commun. 2024, DOI: 10.1038/s41467-023-43492-9).

“Our results show that although the CAA has been very successful in curbing air pollutant emissions, this has not been the case equitably across the sociodemographic gradient in the US,” says study coauthor Marianthi-Anna Kioumourtzoglou, an environmental engineer and epidemiologist at the Columbia University Mailman School of Public Health.

Kioumourtzoglou and coworkers analyzed emission data from the Global Burden of Disease from Major Air Pollution Sources inventory from when the Clean Air Act was passed in 1970 until 2010. They found that air pollution tends to be lower in counties where richer people live. Places with a high proportion of certain racial and ethnic groups, such as Hispanic and Native American people, tend to have higher amounts of air pollution than places with a lower proportion of these groups.

But the trends don’t all fall along the same socioeconomic or racial and ethnic lines, Kioumourtzoglou says. If a county had a higher proportion of Black residents, nitrogen oxide emissions from transportation and commercial sources decreased less than they did in counties with lower proportions of Black residents. Sulfur dioxide from industrial sources and nitrogen oxides from power generation decreased more in the counties where proportions of both White and Black residents were higher. Both types of pollutants decreased less if more Native American people lived in an area.

Other studies have also shown that pollutants aren’t evenly distributed across socioeconomic or racial and ethnic groups, but by looking at what was emitted by county, the new research provides data that are easier for regulators to act on, Kioumourtzoglou says. And while the study shows that the CAA has worked, it also highlights that for some people, it’s not working well enough. Kioumourtzoglou says she hopes the findings will motivate state and federal governments to adjust policies to equitably protect all residents.

The researchers looked at six sources of air pollution, but one of them, agriculture, is not regulated by the CAA, says Oluwatoyin Asojo, a biochemist and associate director for strategic initiatives and global oncology at the Dartmouth Cancer Center. “Agriculture is the only industry that increased emissions between 1970 and 2000, which validates the importance of regulations at the federal level,” she says.