Looking to find the least polluted cities in the United States to get a break from air pollution? Smart Air analyzed 2025 air pollution data for dozens of United States cities to generate the 2025 ranking of the “10 Least Polluted Cities in the United States”.
Scroll down for the full rundown of the least polluted cities in the United States and their annual PM2.5 levels. 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 Least Polluted Cities in the United States
The rankings for the least polluted cities in the world are based on PM2.5 air pollution data from the 12 months prior to the publication date.
1. Bellevue, Washington (3.8 µg/m3)
2. Honolulu, Hawaii (4.1 µg/m3)
3. Colorado Springs, Colorado (4.6 µg/m3)
4. Santa Rosa, California (4.6 µg/m3)
5. Eugene, Oregon (5.2 µg/m3)
6. Lubbock, Texas (5.5 µg/m3)
7. Boise, Idaho (5.6 µg/m3)
8. Vancouver, Washington (5.7 µg/m3)
9. Salinas, California (5.7 µg/m3)
10. Worcester, Massachusetts (5.8 µg/m3)
Read More: The 10 Most Polluted Cities in the United States 2025?
What is the Least Polluted City in the United States?
The lowest PM2.5 cities in the USA show annual average levels ranging from 3.8 to 5.8 µg/m³, indicating very clean air by global standards. Several cities, including Bellevue and Honolulu, meet or fall below the World Health Organization’s recommended guideline of 5 µg/m³, while all cities listed are well below the U.S. national standard of 12 µg/m³. Most of these locations are in coastal or mountain regions such as the Pacific Northwest, Hawaii, and parts of California and Colorado, where favorable geography, lower industrial density, and strong environmental regulations contribute to consistently low particulate pollution levels.
How Air Pollution Was Measured to Find the Least Polluted Cities in the World
The above rankings of the 2025 least polluted cities in the world were ranked based on their average PM2.5 pollution levels from the 12 months prior to the publication date.
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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Portland, OR and areas all around/near are going through a contaminated air crisis, and I think that includes the water too. I just sold my house in Vancouver, WA and moved to nearby Tigard, OR to be near family, and am shocked to discover this! Now I am trying to figure out where else I can move to that has clean air. (makes me very sad) (I’m a retired teacher, and am 81 now, not sure where to go).