County ranking · improvement
Counties with the Biggest Air-Quality Improvement
Where the share of Good air days climbed the most between 2020 and 2025, measured as a percentage-point change so a county's monitoring schedule doesn't skew the result.
- +48.7pp
- Most improved: Solano, California
- 20
- Counties ranked
This ranking measures the change in each county's share of Good air days, not the raw count, so a county that simply added more monitoring days does not appear to "improve." Counties shown were monitored at least 200 days in both 2020 and 2025. Many of the biggest gains follow the unusually smoky 2020 wildfire year, when good days were scarce and have since recovered. See the methodology.
Biggest gain in Good-day share, 2020 → 2025
| # | County | 2020 Good % | 2025 Good % | Change |
|---|---|---|---|---|
| 1 | Solano, California | 50.1% | 98.9% | +48.7pp |
| 2 | Montgomery, Alabama | 19.4% | 65.4% | +46pp |
| 3 | Scotts Bluff, Nebraska | 61.2% | 95.2% | +34pp |
| 4 | San Diego, California | 9% | 42.6% | +33.6pp |
| 5 | Stanislaus, California | 35.8% | 68.3% | +32.5pp |
| 6 | San Miguel, Colorado | 62.8% | 93% | +30.3pp |
| 7 | Ellis, Texas | 65.3% | 92.9% | +27.6pp |
| 8 | Mariposa, California | 54.9% | 81.6% | +26.7pp |
| 9 | Yakima, Washington | 55.2% | 81.1% | +25.9pp |
| 10 | Polk, Florida | 69% | 94.4% | +25.4pp |
| 11 | Colusa, California | 59.7% | 84.9% | +25.2pp |
| 12 | Butte, California | 41.3% | 66.1% | +24.8pp |
| 13 | Glenn, California | 55.4% | 80.2% | +24.8pp |
| 14 | Missaukee, Michigan | 67.9% | 90.8% | +22.8pp |
| 15 | Tippecanoe, Indiana | 48% | 70.7% | +22.7pp |
| 16 | Carter, Oklahoma | 58.3% | 80.9% | +22.6pp |
| 17 | Kay, Oklahoma | 46.7% | 68.4% | +21.7pp |
| 18 | Tehama, California | 59.3% | 80.7% | +21.3pp |
| 19 | Sonoma, California | 79.2% | 100% | +20.8pp |
| 20 | Escambia, Florida | 48.9% | 69.6% | +20.7pp |
Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS) annual county summaries, 2020 and 2025. Good-day share is good days divided by monitored days; only counties monitored 200+ days in both years are ranked.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.