Almost four out of every 10 people in the United States live in a place where air pollution is considered bad enough to put their health at risk, the American Lung Association warned in its latest “State of the Air” report released on Wednesday. That proportion of people — about 39% of the population — had risen sharply since earlier rounds of pollutant data were analyzed for the annual report last year, and the trends were especially pronounced in certain parts of the country.

This year’s air quality report was based on pollution data collected in 2020, 2021 and 2022 by the Environmental Protection Agency. The American Lung Association, a charity organization focused on improving lung health and addressing lung disease,has released “State of the Air” reports annually since 2000.

The new report’s findings show that roughly 131 million Americans were breathing unhealthy air during the three-year monitoring period. That number had jumped by almost 10% since the lung association issued its “State of the Air” report in 2023, when data showed 11.7 million fewer people had been regularly exposed to toxic and potentially deadly pollutants. Echoing longstanding concerns from experts and advocates across the board, the newest findings highlight a disproportionate environmental threat to people of color.

Air quality monitoring

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 EPA. But experts warn that climate change has made air quality harder to manage in spite of policies designed to protect it, especially as growing sections of the country grapple with soaring temperatures, longstanding drought and unprecedented wildfires.

“High ozone days and spikes in particle pollution related to extreme heat, drought and wildfires are putting millions of people at risk and adding challenges to the work that states and cities are doing across the nation to clean up air pollution,” the report’s authors wrote.

Two groups of pollutants were examined: fine particles, which are emitted directly into the air from combustion and some chemical reactions, and ozone, which is usually produced when other air pollutants react with sunlight in the atmosphere. For fine particles, the pollution trends were broken down into short-term and long-term patterns.

The American Lung Association ranked U.S. cities with the worst air quality based on daily particle pollution, annual particle pollution and ozone between 2020 and 2022. The report assigned many cities a failing grade when repeatedly poor readings on the Air Quality Index pushed an area outside the bounds of accepted general health standards. 

Worst cities for particle pollution

Exposure to particulate matter in the air can potentially cause or exacerbate respiratory and cardiovascular problems, according to health officials. Across the country, researchers marked a continued climb over that three-year period in days where particle pollution was considered “very unhealthy” or “hazardous,” compared with years that were monitored previously. Between 2020 and 2022, there were 135 days marked “very unhealthy” and 79 marked “hazardous,” with areas of concern spread across 58 counties housing some 32 million in 10 different states. 

Using an updated baseline standard adopted by the EPA for national air quality, this year’s report showed more than 90 million people were living 119 counties that received failing grades for year-round particle pollution levels. 

At the top of the list of worst U.S. cities for daily and year-round particle pollution was Bakersfield, California, which received the same ranking in last year’s “State of the Air” report. Bakersfield, an industrial city known for agriculture, mining and oil refineries, has been ranked worst for year-round particle pollution five years in a row. 

According to the report, after Bakersfield, the worst cities for year-round particle pollution between 2020 and 2022 were:

• Visalia, California
• Fresno-Madera-Hanford, California
• Eugene-Springfield, Oregon
• San Jose-San Francisco-Oakland, California
• Los Angeles-Long Beach, California
• Sacramento-Roseville, California
• Medford-Grants Pass, Oregon
• Phoenix-Mesa, Arizona
• Fairbanks, Alaska

Cities affected by drought and wildfires were most prevalent on both lists of daily and year-round particle pollution, with eight in California, and two each in Nevada, Oregon and Washington. But even cities where wildfire smoke and drought were less of an issue still suffered from poor air quality, like Pittsburgh, which ranked 19th on the list of cities with the particle pollution year-round and received failing grades for daily particle pollution and ozone as well. 

“In the 25 years that the American Lung Association has been doing our ‘State of the Air’ report, we have seen incredible improvement in our nation’s air quality,” Kevin Stewart, the environmental health director at the American Lung Association, told CBS Pittsburgh. “Unfortunately, more than 131 million people still live in places with unhealthy levels of air pollution, and the Pittsburgh Metro Area is listed as one of the worst places for particle pollution.”

Other cities where particle pollution severely depleted air quality include Indianapolis, Detroit, Houston, Kansas City, Cincinnati, Chicago, Oklahoma City, Augusta, Georgia, and Corpus Christi, Texas.

Worst cities for ozone 

Although ozone in the upper atmosphere protects Earth, high levels of the gas farther down can be harmful to human health and the environment. Experts have noted in particular that inhaling unhealthy concentrations of ozone in the air can cause a range of breathing problems and even weaken the lungs against infection. 

The American Lung Association’s annual reports have plotted a more optimistic, downward trend in ozone concentration nationwide in the last 20 years, as environmental controls forced a transition “away from coal-fired power pants, the dirtiest fossil fuel, and towards clean renewable sources of energy,” the latest report said. But it still showed about 100 million people across 26 states living in places where ozone levels received a failing grade for air quality. The report again noted that extreme heat, lack of precipitation and wildfires associated with climate change, largely across western states, have undermined attempts to cut back on emissions.

Los Angeles — infamous for its smog, which is mainly composed of ozone — ranked as the worst city for ozone pollution in the country, as it has on all but one “State of the Air” report. After Los Angeles, the most polluted cities for ozone were:

• Visalia, California
• Bakersfield, California
• Fresno-Madera-Hanford, California
• Phoenix-Mesa, Arizona
• Denver-Aurora, Colorado
• Sacramento-Roseville, California
• San Diego-Chula Vista-Carlsbad, California
• Salt Lake City-Provo-Orem, Utah
• Houston-The Woodlands, Texas

Of the 25 worst metropolitan areas for ozone pollution, 10 were in California, and others in just six states — Arizona, Colorado, Nevada, New Mexico, Texas and Utah — held 12 more spots. Only three cities in the eastern U.S. made the list, which were New York, Chicago and Grand Rapids, Michigan.