New air quality data released this year shows a wide gulf between the cleanest and most polluted states in the country, with sparsely populated Western and Pacific states such as Wyoming and Hawaii consistently ranking among the healthiest for air quality, while densely populated, industrial states including California, Pennsylvania and Ohio continue to post some of the worst readings in the nation.

Two separate analyses released in early 2026, using slightly different methodologies, arrived at broadly similar conclusions about which states offer the cleanest air. An analysis published in March, based on fine particulate pollution, or PM2.5, levels averaged from 2022 through 2024, found that the U.S. average stood at 8.8 micrograms per cubic meter, well above the World Health Organization's air quality guideline of 5 micrograms per cubic meter, meaning the average American is breathing air that falls short of internationally recognized health standards.

According to that analysis, Wyoming posted the cleanest air in the country, a result researchers attributed largely to the state's vast, sparsely populated landscape and minimal industrial development. Wyoming's city of Casper recorded the lowest year-round particle pollution of any metro area tracked in the report, while the state capital, Cheyenne, ranked eighth overall among individual cities nationwide. Hawaii ranked second among states for particle pollution, posting a reading of 4.7 micrograms per cubic meter, a result researchers linked to the state's low population density combined with strong prevailing winds and consistent rainfall that help disperse pollutants before they can accumulate.

At the opposite end of that same ranking, California posted........

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