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.

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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.

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