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By Jasmine Laws
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Cities in California make up a significant proportion of the country's most polluted places when it comes to air quality, according to the American Lung Association (ALA).
The organization's 2025 "State of the Air" report reveals that Bakersfield, Visalia, and Fresno-Madera-Hanford ranked as the top three metropolitan areas with the worst year-round particle pollution.
The findings were based on air quality data collected between 2021 and 2023, and looked at ground-level ozone air pollution (also known as smog), along with year-round and short-term spikes in particle pollution (soot).
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Why It Matters
Microscopic pollutants primarily come from vehicle emissions, industrial facilities, and wildfires. They are linked to serious health issues including asthma, heart disease, and premature death.
As President Donald Trump pushes to repeal several clean air and water regulations, the ALA has warned that this could deal a severe blow to U.S. public health.
What To Know
The ALA's report revealed that 156 million Americans, or 46 percent of the U.S. population, lived in an area that received a failing grade for at least one measure of air pollution between 2021 and 2023. Meanwhile, a total of 42.5 million Americans lived in counties with failing grades for all three types of air pollution measured.
The cities with the worst year-round particle pollution included Bakersfield-Delano, Visalia and Fesno-Hanford-Corcoran. Other highly polluted cities outside of California included Eugene-Springfield in Oregon, and Detroit-Warren-Ann Arbor in Michigan.
The cities with the worst short-term particle pollution were Bakersfield-Delano, Fairbanks-College and Eugene-Springfield.
The 25 most polluted cities for year-round particle pollution, according to the ALA's report, were:
1: Bakersfield-Delano, CA
2: Visalia, CA
3: Fresno-Hanford-Corcoran, CA
4: Eugene-Springfield, OR
5: Los Angeles-Long Beach, CA
6: Detroit-Warren-Ann Arbor, MI
6: San Jose-San Francisco-Oakland, CA
8: Houston-Pasadena, TX
9: Cleveland-Akron-Canton, OH
10: Fairbanks-College, AK
11: Indianapolis-Carmel-Muncie, IN
12: Pittsburgh-Weirton-Steubenville, PA-OH-WV
13: Chicago-Naperville, IL-IN-WI
14: Cincinnati-Wilmington, OH-KY-IN
14: Sacramento-Roseville, CA
16: Brownsville-Harlingen-Raymondville, TX
17: Medford-Grants Pass, OR
17: Missoula, MT
17: St. Louis-St. Charles-Farmington, MO-IL
20: Kalamazoo-Battle Creek-Portage, MI
20: Phoenix-Mesa, AZ
22: Texarkana, TX-AR
23: El Centro, CA
23: Yakima, WA
25: Spokane-Spokane Valley-Coeur d'Alene, WA-ID
The top 25 most polluted cities for short-term particle pollution were:
1: Bakersfield-Delano, CA
2: Fairbanks-College, AK
3: Eugene-Springfield, OR
3: Visalia, CA
5: Fresno-Hanford-Corcoran, CA
6: Reno-Carson City-Gardnerville Ranchos, NV-CA
7: Los Angeles-Long Beach, CA
8: Yakima, WA
9: Seattle-Tacoma, WA
10: Sacramento-Roseville, CA
11: Medford-Grants Pass, OR
11: San Jose-San Francisco-Oakland, CA
11: Spokane-Spokane Valley-Coeur d'Alene, WA-ID
14: Bismarck, ND
15: Missoula, MT
16: Pittsburgh-Weirton-Steubenville, PA-OH-WV
16: Redding-Red Bluff, CA
18: Fargo-Wahpeton, ND-MN
19: Minot, ND
20: Helena, MT
21: Indianapolis-Carmel-Muncie, IN
22: Detroit-Warren-Ann Arbor, MI
22: Lancaster, PA
22: Logan, UT-ID
25: Salt Lake City-Provo-Orem, UT-ID
These rankings capture areas most affected by episodic spikes in particle pollution, often driven by wildfires or sudden extreme heat.
What People Are Saying
Harold Wimmer, the president and CEO of the ALA, said in a statement: "This year's report shows the dramatic impact that air pollution has on a growing number of people. Even as more people are breathing unhealthy air, the federal staff, programs and policies that are supposed to be cleaning up pollution are facing rollbacks, restructuring and funding challenges. For decades, the U.S. Environmental Protection Agency (EPA) has worked to ensure people have clean air to breathe, from providing trustworthy air quality forecasts to making sure polluters who violate the law clean up. Efforts to slash staff, funding and programs at EPA are leaving families even more vulnerable to harmful air pollution. We need to protect EPA."
Peter DeCarlo, a professor of environmental health and engineering at the John Hopkins Whiting School of Engineering, Maryland, told Newsweek: "Air pollution levels are influenced by a number of factors including population, geography, and typical weather. The more people you have in an area, you typically have more emissions, and therefore higher levels of air pollution. Geography or land type is really important as well. If you have mountains or valleys, pollution can get trapped in an area and build up to higher concentrations; in flatter areas air pollution travels away with the wind. Finally, sunny and warmer weather can lead to faster chemical reactions in the air which generate higher levels of air pollutants like ozone and some types of particulate matter which are no directly emitted but formed from those chemical reactions."
He added: "California has all of the ingredients to produce higher levels of air pollution: high population, mountains and the central valley, and sunshine and warmth."
Mark Jacobson, professor of civil and environmental engineering and director of the Atmosphere/Energy Program at Stanford University, told Newsweek: "Los Angeles air pollution is due to the fact that the Los Angeles basin is surrounded by mountains to the west and north, and a daily breeze blows pollutants from west to east toward the mountains. Because a high pressure system sits over the basin 95 percent of the year, air is trapped below the top of the mountains under the inversion, and there are only three passes (Banning, Tajon, and Cajon) through which pollution can get through. So, pollution builds up in the basin over several days, creating an episode until strong winds or a weak high pressure system allows the pollution to clear out."
He added: "In Denver, ozone forms readily because Denver is elevated so receives more UV light than lower-altitude cities. Salt Lake City is surrounded by mountains, so pollutants build up there and don't escape easily. Dallas and Houston are exposed to heavy UV radiation due to the fact they are at lower latitudes than many U.S. cities and in locations with few clouds. The UV light cooks up ozone readily from the vehicle and other emissions."
What Happens Next
In March, the Environmental Protection Agency (EPA) announced its plan to undo more than two dozen major environmental regulations dealing with greenhouse gas emissions, toxic air pollution and waste from fossil fuel extraction.
The Environmental Protection Network (EPN) subsequently warned that the rollbacks could result in 200,000 additional premature deaths and cause more than 100 million preventable asthma attacks through 2050.
Update 04/24/25, 3:20 a.m. ET: This article has been updated with comment from Mark Jacobson.
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