Looking to find the most polluted cities in the United States? Smart Air analyzed 2025 air pollution data for dozens of United States cities to generate the ranking of the “10 Most Polluted Cities in the United States”.
Scroll down for the full rundown of the most polluted cities in the United States and their annual PM2.5 levels. The annual average PM2.5 in micrograms (µg/m3) is also given. For reference, the WHO recommended annual limit is 5 micrograms.
Rankings: 10 Most Polluted Cities in the United States in 2025
The rankings for the most polluted cities in the US are based on PM2.5 air pollution data from 2025.
1. El Paso, Texas (15.9 µg/m3)
2. Pomona, California (15 µg/m3)
3. Bakersfield, California (13.5 µg/m3)
4. Ontario, California (13.1 µg/m3)
5. Los Angeles, California (12.4 µg/m3)
6. Riverside, California (12.2 µg/m3)
7. Long Beach, California (12.2 µg/m3)
8. Pasadena, Texas (11.8 µg/m3)
9. Torrance, California (11.7 µg/m3)
10. Huntington Beach, California (11.6 µg/m3)
Read More: The 10 Least Polluted Cities in the United States 2025?
What is the Most Polluted State in the United States in 2025?
Most of these cities are concentrated in Southern California, where heavy traffic, port activity, industrial emissions, and basin geography contribute to higher particulate levels. In addition, seasonal wildfire smoke plays a significant role, particularly in Western states, where intense fire seasons can sharply increase PM2.5 concentrations and raise annual averages. Although these levels are high relative to other U.S. cities, they remain lower than many global pollution hotspots, but still exceed the WHO guideline of 5 µg/m³.
Read more: How Wildfires in California Affect Air Quality
How Air Pollution Was Measured to Find the Most Polluted Cities in the US
The above rankings of the 2025 most polluted cities in the US were ranked based on their average PM2.5 pollution levels in 2025.
These small pollutants are under 2.5 micrograms in width and are considered to be one of the more dangerous pollutants due to their ability to enter deep into the lungs and bloodstream.
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You need to put Lafayette Indiana it’s a smaller city and everyone is sick year round with RSV and allergies due to several crappy factories that put a ton of pollution in the air, such as Tate and Lyle, Staleys and others.