The 10 U.S. Cities With the Cleanest Air

By Sam Stebbins  •  April 27, 2026
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Photo by Cristina Anne Costello on Unsplash

Carbon dioxide emissions – a byproduct of fossil fuel consumption – have surged in recent decades. According to data from the World Bank, 39.6 billion tons of C02 were released into Earth’s atmosphere in 2024, a more than 150% increase from 1970. The connection between carbon emissions and climate change is well established, but other hazardous by-products of fossil fuel consumption also pose an imminent health risk to millions of people across the globe. 

Many of the fuels that power the modern world – gasoline, diesel, coal, and even wood – emit harmful air pollution when burned. These pollutants include PM2.5, a category of fine particulate matter measuring 2.5 micrometers or less, about one-30th the diameter of a human hair. Long term exposure to high concentrations of PM2.5 has been linked to a range of conditions including heart disease, lung cancer, pneumonia, stroke, and diabetes. According to a joint study conducted by the Health Effects Institute and the Institute for Health Metrics and Evaluation, PM2.5 exposure contributed to over 4.1 million deaths worldwide in 2019, or about 62% of all deaths linked to air pollution. 

Despite increased fossil fuel consumption, PM2.5 pollutants have been falling in recent years. World Bank data shows that average global PM2.5 concentrations fell from 43 micrograms per cubic meter to 31 between 2013 and 2020. Still, even at these improved levels, global PM2.5 concentrations are about six times higher than those recommended by the World Health Organization.

In the United States, the average concentration of PM2.5 was about 8 micrograms per cubic meter in 2020 – well below the global average but still higher than WHO recommendations. Notably, however, there are several major U.S. metro areas where levels of air pollution are so low that PM2.5 poses virtually no public health risk. 

Using data from the American Lung Association’s 2026 State of the Air Report, Climate Crisis 247 identified the 10 U.S. cities with the cleanest air. We ranked all metro areas included in the study on the average concentration of PM2.5 between 2022 and 2024. Supplemental data on the number of days per year when levels of PM2.5 are deemed unhealthy represent a weighted average, calculated and reported by the ALA. Population density figures were calculated using data from the U.S. Census Bureau’s 2024 American Community Survey. Only the 10 U.S. metro areas with the cleanest air are ranked. 

Among the metro areas on this list, annual PM2.5 concentrations are as low as 3.2 micrograms per cubic meter. Air pollution tends to be worse in densely populated areas, due to factors including elevated traffic volume, industrial activity, and residential energy use. Perhaps not surprisingly, most metro areas on this list have a lower population density than the national average of about 96 people per square mile. Most of these cities are also located in low population density states.  

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Photo by Jesse on Unsplash

10. Bangor, Maine

  • Average annual concentration of PM2.5: 5.0 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0 days per year
  • Bangor Metro Area population density: 46.2 people per sq. mile (26th lowest of 393 U.S. metro areas)
  • Population density across Maine: 45.6 people per sq. mile (13th lowest of 50 states)
  • Metro area population: 156,840

9. Grand Junction, Colorado

  • Average annual concentration of PM2.5: 4.9 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0.3 days per year
  • Grand Junction Metro Area population density: 48.4 people per sq. mile (31st lowest of 393 U.S. metro areas)
  • Population density across Colorado: 57.5 people per sq. mile (14th lowest of 50 states)
  • Metro area population: 161,260

8. Cheyenne, Wyoming

  • Average annual concentration of PM2.5: 4.7 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 1.5 days per year
  • Cheyenne Metro Area population density: 37.9 people per sq. mile (21st lowest of 393 U.S. metro areas)
  • Population density across Wyoming: 6.1 people per sq. mile (2nd lowest of 50 states)
  • Metro area population: 101,783

7. Anchorage, Alaska

  • Average annual concentration of PM2.5: 4.7 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0.3 days per year
  • Anchorage Metro Area population density: 15.4 people per sq. mile (5th lowest of 393 U.S. metro areas)
  • Population density across Alaska: 1.3 people per sq. mile (the lowest of 50 states)
  • Metro area population: 407,213

6. St. George, Utah

  • Average annual concentration of PM2.5: 4.4 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0 days per year
  • St. George Metro Area population density: 85.7 people per sq. mile (67th lowest of 393 U.S. metro areas)
  • Population density across Utah: 42.4 people per sq. mile (11th lowest of 50 states)
  • Metro area population: 207,943

5. Burlington-South Burlington-Barre, Vermont

  • Average annual concentration of PM2.5: 4.3 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 1.5 days per year
  • Burlington-South Burlington-Barre Metro Area population density: 183.7 people per sq. mile (189th lowest of 393 U.S. metro areas)
  • Population density across Vermont: 70.4 people per sq. mile (20th lowest of 50 states)
  • Metro area population: 229,550

4. Urban Honolulu, Hawaii

  • Average annual concentration of PM2.5: 4.2 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0.3 days per year
  • Urban Honolulu Metro Area population density: 1,662.4 people per sq. mile (5th highest of 393 U.S. metro areas)
  • Population density across Hawaii: 225.2 people per sq. mile (14th highest of 50 states)
  • Metro area population: 998,747

3. Kahului-Wailuku, Hawaii

  • Average annual concentration of PM2.5: 4.0 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0.8 days per year
  • Kahului-Wailuku Metro Area population density: 139.6 people per sq. mile (130th lowest of 393 U.S. metro areas)
  • Population density across Hawaii: 225.2 people per sq. mile (14th highest of 50 states)
  • Metro area population: 163,769

2. Casper, Wyoming

  • Average annual concentration of PM2.5: 3.4 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0.7 days per year
  • Casper Metro Area population density: 15.1 people per sq. mile (3rd lowest of 393 U.S. metro areas)
  • Population density across Wyoming: 6.1 people per sq. mile (2nd lowest of 50 states)
  • Metro area population: 80,410

1. Bozeman, Montana

  • Average annual concentration of PM2.5: 3.2 micrograms per cubic meter
  • Days with unhealthy concentrations of PM2.5 (weighted average): 0.3 days per year
  • Bozeman Metro Area population density: 48.7 people per sq. mile (32nd lowest of 393 U.S. metro areas)
  • Population density across Montana: 7.8 people per sq. mile (3rd lowest of 50 states)
  • Metro area population: 126,984


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