Weakening or rolling back longstanding environmental regulations would worsen the problem, the American Lung Association assessment says.

By Rebecca Dzombak

April 23, 2025, 12:01 a.m. ET

At least 156 million Americans, about 46 percent of the population, live with unsafe levels of ozone, particulate pollution or both, according to the American Lung Association’s annual State of the Air report.

Plans by the Trump administration to loosen environmental regulations and cut funding for air quality research would make matters worse, the report says.

“The biggest thing that has saved patients’ lives in regard to lung health and overall health is the Clean Air Act,” said Panagis Galiatsatos, a pulmonologist at the Johns Hopkins School of Medicine and spokesman for the lung association. “Clearly, legislation is needed because that’s what dictates the air quality you breathe.”

The report analyzed ozone and particulate pollution levels between 2021 and 2023, a period that included the worst wildfire season on record in Canada. The report ranked pollution levels in counties and cities from best to worst, using a scale from F to A.

Air quality in the United States has been generally improving since the Clean Air Act was enacted in 1970, with levels of key pollutants dropping by nearly 80 percent. But millions of Americans still breathe polluted air every day, leading to both acute and chronic health conditions that, in some cases, increase the risk of early death.

At least 156.1 million people live with air that got the poorest grade of F for at least one pollutant, and at least 42 million people live in counties that failed all three pollutant standards. Of the 885 counties with air quality monitoring data, 480 counties failed at least one of the three measures.

The Biden administration aimed to improve air quality with measures like tighter rules for vehicle emissions and on mercury and carbon emissions from power plants. The Trump administration is already working to reverse those regulations.

President Trump has also directed the government to increase the mining and use of coal, including through an executive order earlier this month.

“We’re slashing unnecessary regulations that targeted the beautiful, clean coal,” Mr. Trump said when the order was signed. “I’m also directing Secretary Wright to use billions of dollars of federal funding to invest in the next generation of coal technology,” he added, referring to Energy Secretary Chris Wright.

The report also found that people of color are more than twice as likely to live in a community with high ozone and particulate pollution, compared with white people. Hispanic communities are three times as likely to be exposed to air that had at least one poor air quality measurement.

Those findings aren’t surprising, said Regan Patterson, an environmental engineer and environmental justice researcher at the University of California, Los Angeles. But documenting continued disparities in who is exposed to air pollution is critical to motivate policy change, she said.

“We have clean air policies, and they have led to improvements,” Dr. Patterson said. “It’s important to see if these have reduced, or even eliminated, air quality exposure disparities, and we are seeing that they have not.”

Overall, exposure of Americans to both ozone and particulate pollution went up. More than 125 million people live in counties with unhealthy levels of ozone, an increase of 24.6 million from the previous report, which covered 2020-22. “The severity of the problem and the abruptness of the change are unprecedented,” according to the authors.

Ninety-three more counties failed the ozone measure than did in the last report, and 10 counties swung to an F from an A.

The wildfires in Canada drove much of that change: Smoke traveled south and east, and the ozone burden shifted to the Plains, Midwest and Eastern United States.

While the hot and dry weather that fueled the fires in Canada last year was extraordinary when compared with historical records, climate projections suggest such conditions will become common in the 2050s if the world continues on the current trajectory of global warming.

As in previous years, California had the most metropolitan areas with high levels of ozone pollution but Chicago, New York and St. Louis joined the list of the most ozone-polluted cities.

For particulate pollution smaller than 2.5 microns across, known as PM2.5, the report analyzed both daily and annual pollution levels. Daily reports capture short-term changes, such as spikes in pollution from wildfire smoke, while the annual level reflects a more sustained level of exposure.

Daily PM2.5 exposure affects at least 77 million people, the largest population affected in the last 16 years, an increase largely attributable to the Canadian wildfires. About 85 million people live in counties that do not meet the EPA’s standards for annual exposure to PM2.5.

Only two cities met the report’s qualifications for clean air this year: Bangor, Maine, and San Juan, P.R. These cities had no days with extremely high ozone or PM2.5 pollution and ranked in the 25 cities with the lowest annual PM2.5 levels.

While the report aims to paint a complete picture of air quality around the country, the data has limitations. Roughly two-thirds of counties in the United States lack air quality monitoring for ozone or particulate pollution. A study published Tuesday in Proceedings of the National Academy of Sciences estimates 50 million people, or more than 15 percent of the United States’ population live in places without reliable air quality monitoring.

“Any estimate we have about health and its relationship with pollution is an underestimate,” said Nelson Roque, who studies environmental health at Pennsylvania State University and was lead author of the study.

What’s the Best Thing I Can Do for the Planet?

A resurgence in coal power plants would increase particulate pollution and carbon emissions, as well as toxic components such as mercury.

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