Among counties with populations over 100,000, these have the cleanest air based on EPA monitoring data. Grades based on 3-year average median Air Quality Index (2021–2023). Lower AQI is better.
A clear pattern emerges: counties with top-tier air quality often hug coastlines or nestle near mountain ranges. Washington and Hawaii, with five and three counties respectively, exemplify this, benefiting from prevailing winds that disperse pollutants and less concentrated industrial activity. New York also makes a strong showing with seven counties, many of which are upstate, away from major urban centers, suggesting that proximity to natural ventilation plays a significant role in maintaining clean air.
Columbiana County, Ohio, claiming the #1 spot, might surprise many, given its location in a state often associated with heavy industry. However, its position along the Ohio River and its relatively rural character, even for a large county, likely contribute to its exceptional air quality. This highlights that even in industrial regions, specific geographic and economic factors can create pockets of remarkably clean air, defying broader state-level perceptions.
Mohave County, Arizona, at #2, presents an interesting dynamic. Despite experiencing robust population and GDP growth, it maintains excellent air quality. This suggests that its vast desert landscape, low population density relative to its size, and limited heavy industry allow for efficient dispersion of any localized emissions, proving that growth doesn't always have to come at the expense of environmental health in certain geographic contexts.
| # | County | BTI Score | Air Grade | Median AQI | Good Days |
|---|---|---|---|---|---|
| 01 | Columbiana County OH | 42 | A | 13 | 99% |
| 02 | Mohave County AZ | 92 | A | 17 | 97% |
| 03 | Maui County HI | 62 | A | 21 | 99% |
| 04 | Cowlitz County WA | 82 | A | 21 | 91% |
| 05 | Monroe County MI | 36 | A | 23 | 89% |
| 06 | Thurston County WA | 66 | A | 25 | 91% |
| 07 | Kitsap County WA | 75 | B+ | 25 | 91% |
| 08 | Deschutes County OR | 37 | B+ | 25 | 78% |
| 09 | Lubbock County TX | 30 | B+ | 27 | 85% |
| 10 | Hawaii County HI | 91 | B+ | 28 | 91% |
| 11 | Oneida County NY | 80 | B+ | 28 | 85% |
| 12 | Bonneville County ID | 61 | B+ | 28 | 85% |
| 13 | Humboldt County CA | 1 | B+ | 28 | 87% |
| 14 | Pueblo County CO | 14 | B+ | 29 | 86% |
| 15 | Grant County WA | 6 | B+ | 29 | 81% |
| 16 | Potter County TX | 89 | B+ | 29 | 86% |
| 17 | Honolulu County HI | 73 | B+ | 29 | 97% |
| 18 | Skagit County WA | 87 | B+ | 30 | 91% |
| 19 | Whatcom County WA | 23 | B+ | 30 | 91% |
| 20 | Kootenai County ID | 91 | B+ | 31 | 75% |
| 21 | Nassau County NY | 33 | B+ | 31 | 80% |
| 22 | Saratoga County NY | 61 | B+ | 31 | 97% |
| 23 | Jefferson County NY | 85 | B+ | 32 | 96% |
| 24 | Ascension Parish LA | 19 | B+ | 32 | 91% |
| 25 | Clackamas County OR | 76 | B+ | 33 | 84% |
| 26 | Oswego County NY | 98 | B+ | 33 | 96% |
| 27 | Gallatin County MT | 32 | B+ | 33 | 79% |
| 28 | Rockwall County TX | 4 | B+ | 33 | 94% |
| 29 | Manatee County FL | 58 | B+ | 33 | 96% |
| 30 | Kennebec County ME | 16 | B+ | 33 | 89% |
| 31 | St. Lucie County FL | 97 | B+ | 34 | 98% |
| 32 | Penobscot County ME | 71 | B+ | 34 | 87% |
| 33 | Highlands County FL | 69 | B+ | 34 | 96% |
| 34 | Linn County OR | 41 | B+ | 34 | 73% |
| 35 | Yellowstone County MT | 21 | B+ | 34 | 78% |
| 36 | Niagara County NY | 87 | B+ | 34 | 94% |
| 37 | Flagler County FL | 73 | B+ | 34 | 97% |
| 38 | Dutchess County NY | 57 | B+ | 34 | 95% |
| 39 | Bay County MI | 50 | B+ | 34 | 75% |
| 40 | Indian River County FL | 89 | B+ | 34 | 97% |
| 41 | Osceola County FL | 82 | B+ | 34 | 95% |
| 42 | Androscoggin County ME | 53 | B+ | 34 | 86% |
| 43 | Gregg County TX | 45 | B+ | 34 | 88% |
| 44 | San Mateo County CA | 9 | B+ | 34 | 83% |
| 45 | Columbia County GA | 7 | B+ | 34 | 97% |
| 46 | Hendricks County IN | 32 | B+ | 35 | 94% |
| 47 | Maury County TN | 3 | B+ | 35 | 77% |
| 48 | Kent County RI | 54 | B+ | 35 | 87% |
| 49 | Clark County WA | 49 | B+ | 35 | 78% |
| 50 | Brazoria County TX | 23 | B+ | 35 | 86% |