Nearly half of U.S. kids are breathing unhealthy air, report says. These are the cleanest and most polluted cities.

For 152 million Americans, including nearly half of the nation’s children and adolescents, simply breathing the air where they live can be harmful. According to the latest report from the American Lung Association Air Condition According to one report, 44% of the U.S. population resides in areas with unhealthy levels of pollution, including 33 million under the age of 18.

Experts have been warning for years that children are particularly sensitive to the consequences of exposure to pollution. Young people are considered more vulnerable because they have developing lungs, relatively large air intake requirements compared to adults and spend more time outdoors.

“We recognize that there is a link between air pollution and children’s exposure to chronic diseases,” said Kevin Stewart, director of environmental health at the American Lung Association and one of the report’s co-authors. “The problems aren’t necessarily immediate, just sending a child with asthma to the hospital. It can also affect the induction of asthma in children who normally wouldn’t have gotten it, or reduce lung function over their lifetime because they were exposed as children.”

The new report assesses air quality in different regions of the country by measuring the presence of ozone and polluting particles in the atmosphere, over short and long term periods. Ozone pollution is also known as smog; particle pollution is known as soot.

Counties were ranked based on the amount of smog and soot researchers detected, as well as how long the pollutants had been present. The report is based on data collected between 2022 and 2024. As its authors noted, air quality conditions during this two-year period appeared to show improvements in some areas and setbacks in others.

Nearly 4 million more people in the United States breathed unhealthy levels of smog between 2022 and 2024 compared to the period between 2021 and 2023, the period used to compile last year’s data. Air Condition report. And, although the latest report showed more than 61 million people living in counties with an “F” rating for unhealthy short-term spikes in soot pollution, and an additional 75 million living in counties with an “F” rating for year-round soot pollution, both numbers were better than before.

Stewart called it “good news,” but “at the same time, there are still obvious problems in some parts of the country.” Southern and southwest states, as well as a number of metro areas in Texas in particular, have seen notable particle pollution, he said.

Most polluted American cities

Bakersfield, California, continues to rank first on the American Lung Association’s list of cities with the worst particle pollution throughout the year. It also ranks third among the cities most polluted by particles and ozone in the short term.

The five most polluted cities, according to the American Lung Association report, are:

1. Bakersfield-Delano, California
2. Brownsville-Harlingen-Raymondville, Texas
3. Eugene-Springfield, Oregon
4. Fresno-Hanford-Corcoran, California
5. San Diego-Chula Vista-Carlsbad, California (tied with Visalia, California)

Another major year air quality reviewfrom Swiss technology company IQAir, placed El Paso, Texas, and Los Angeles, California, among the most polluted regions in the United States. This report examined pollution around the world and found that concentrations in the United States increased by 3% between 2024 and 2025.

The cleanest American cities

The American Lung Association report also ranked the U.S. cities with the cleanest air. When it comes to year-round particle pollution, Bozeman, Montana tops the list ahead of Casper, Wyoming, which held the top spot in 2025.

The five cleanest cities are:

1. Bozeman, Montana
2. Casper, Wyoming
3. Kahului-Wailuku, Hawaii
4. Urban Honolulu, Hawaii
5. South Burlington Burlington-Barre, Vermont

Data centers

In addition to more traditional sources of pollution, like power plants and vehicle exhaust, the new air quality report warns that data centers used to train, maintain and operate artificial intelligence models also increasingly contribute to air pollution.

“We’re trying to alert the public to make sure that any data centers that are created use state-of-the-art pollution controls,” whether they burn fossil fuels or rely on backup generators as their primary source of power, Stewart said.

The American Lung Association also cited policies of the Trump administration, which faces pushback this year, following his decision to deregulate emissions and repeal the historic scientific discovery which linked greenhouse gases to human health problems.

Known as a “hazard statement,” the policy was rescinded by the Environmental Protection Agency in February, when President Trump announced that greenhouse gases emitted by cars, power plants and other large-scale sources would no longer be regulated by the federal government. Emissions of common air pollutants have fallen massively since the Clean Air Act was enacted in 1970, according to the EPA, but additional data shows they have increased again in recent years.

“Contrary to its mission, EPA has recently acted to weaken, delay, or revoke key health protections, which will leave American children more exposed and more vulnerable to the consequences of many different pollutants, including ozone and particle pollution,” the report’s authors wrote, adding that the agency “must not devalue the benefits of eliminating deadly pollution from the air children breathe.”