A new report on air quality across the United States offered a cloudy prognosis on the long-term health of about 156 million residents who live in areas that received an "F" in smog and soot pollution. 

The American Lung Association's annual State of the Air report, which looked at the latest air quality data from 2021 to 2023, concluded that 25 million more people are breathing "unhealthy levels of air pollution" compared to last year. According to the report, around 46% of people in the U.S. live in an area that received a failing grade in at least one of the three measures that were studied: short-term particle pollution, year-round particle pollution and ozone pollution.

Since the Clean Air Act was signed into law in 1970, emissions of the six most common air pollutants have fallen by 78%, according to the Environmental Protection Agency — but recent analyses show air pollution has been on the rise in recent years.

"Since the act passed, the air pollution has gone down overall," Laura Kate Bender, an assistant vice president at the American Lung Association, told CBS News. "The challenge is that over the last few years, we're starting to see it tick back up again and that's because of climate change, in part. Climate change is making some of those conditions for wildfires and extreme heat that drive ozone pollution worse for a lot of the country."

The most polluted and cleanest U.S. cities

For the sixth year in a row, Bakersfield, California, remained the city with the worst year-round particle pollution and short-term particle pollution, according to the report. The industrial city — known for agriculture, mining and oil refineries — also ranked third for worst high ozone days.

Conversely, the city ranked first in the American Lung Association's top 25 cleanest U.S. cities by year-round particle is Casper, Wyoming, which has less than 80,000 residents compared to Bakersfield's nearly 914,000 population.

Here's the American Lung Association's latest list of the top 10 cities with the worst year-round particle pollution:

1. Bakersfield-Delano, California
2. Visalia, California
3. Fresno-Hanford-Corcoran, California
4. Eugene-Springfield, Oregon
5. Los Angeles-Long Beach, California
6. Detroit-Warren-Ann Arbor, Michigan
7. San Jose-San Francisco-Oakland, California
8. Houston-Pasadena, Texas
9. Cleveland-Akron-Canton, Ohio
10. Fairbanks-College, Arkansas

Climate change and regulations roll back

Prior years of reporting found that the worst of the nation's air quality was concentrated in western states, but the new report released Wednesday said the concentration of poor air has started to shift east.

Extreme heat, lack of precipitation and wildfires associated with climate change continue to play a growing part in worsening the air quality across the U.S. and exposing a growing proportion of Americans to pollutants, the report said. It cited a 2023 deadly heat wave and smoke from Canada's worst wildfire season as contributors to worsened levels of air pollution in central and eastern states. 

"I think we knew that the wildfire smoke would have an impact on air quality in the United States," Kevin Stewart, the American Lung Association's environmental health director, told CBS Philadelphia. "I think we were surprised at the Lung Association by how strong the effect was, especially in the northeastern quadrant of the continental United States."

Last month, the EPA announced it will roll back or change 31 environmental rules and regulations, including revisions of national air quality standards for particulate matter, emission standards for industrial air pollutants and regulations restricting vehicle emissions. The proposed cuts are putting more than five decades of progress at risk, Kate Bender said.

"Unfortunately, we see that everything that makes our air quality better is at risk," she said. "The EPA is at risk — the agency that is protecting our health — through staff cuts, funding cuts. The regulations that have cleaned up our air over time are at risk of being cut. If we see all those cuts become reality, it's gonna have a real impact on people's health by making the air they breathe dirtier."

EPA Administrator Lee Zeldin argued that the deregulation will instead drive "a dagger straight into the heart of the climate change religion to drive down cost of living for American families, unleash American energy, bring auto jobs back to the U.S. and more."

Zeldin told senior White House correspondent Weijia Jiang on "Face the Nation" that he can "absolutely" guarantee that Trump administration deregulations won't have adverse health impacts on people and the environment.

What are the health effects of air pollution?

Both ozone and particle pollution can cause a wide range of health problems that lead to premature death, according to the American Lung Association. The effects of bad air quality have been extensively studied and shown to cause asthma and heart attacks, strokes, lung cancer and impaired cognitive function later in life.

"The air pollutants covered in this report are widespread and can impact anyone's health," Kezia Ofosu Atta, advocacy director for the Lung Association in Michigan, told CBS Detroit. 

"This air pollution is causing kids to have asthma attacks, making people who work outdoors sick and unable to work, and leading to low birth weight in babies," Ofosu Atta said, who urged lawmakers to take action to improve the city's air, which ranked sixth in the nation for year-round pollution.

The American Lung Association's report noted that Black people are more like to suffer the serious health effects of air pollution due to the long history of systemic racism in the U.S., including segregation and decision-makers finding it easier to place sources of pollution such as power plants, industrial facilities, landfills and highways in economically disadvantaged communities of color.

Jerod Dabne contributed reporting.