County ranking · 2020→2025 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.
- +49.2pp
- Most improved: Solano, California
- 20
- Counties ranked
Solano County, California gained the most Good-day share (+49.2pp) from 2020 to 2025 among 20 ranked counties
This ranking compares each county's share of Good air days in 2020 versus 2025 using EPA AQS annual summaries. Only counties monitored at least 200 days in both years qualify. Many top gains follow recovery from the smoky 2020 wildfire season; this is trend data, not a live AirNow reading.
Data source EPA Air Quality System (AQS)
- Solano County, California moved from 50% to 99.2% Good-day share (+49.2pp), the largest gain in the cohort.
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.
from the compiled EPA AQS release in this database.
Biggest gain in Good-day share, 2020 → 2025
| # | County | 2020 Good % | 2025 Good % | Change |
|---|---|---|---|---|
| 1 | Solano, California | 50% | 99.2% | +49.2pp |
| 2 | Montgomery, Alabama | 19.4% | 63.8% | +44.4pp |
| 3 | Mono, California | 50% | 90.1% | +40.1pp |
| 4 | Missoula, Montana | 42.3% | 81.6% | +39.3pp |
| 5 | Scotts Bluff, Nebraska | 61.2% | 95.8% | +34.6pp |
| 6 | Mariposa, California | 53.3% | 80.6% | +27.3pp |
| 7 | Polk, Florida | 69% | 95.5% | +26.5pp |
| 8 | Calaveras, California | 56.6% | 82.2% | +25.6pp |
| 9 | Glenn, California | 54.9% | 80% | +25.1pp |
| 10 | Escambia, Florida | 48.9% | 73.7% | +24.8pp |
| 11 | Butte, California | 40.7% | 65.2% | +24.5pp |
| 12 | Kay, Oklahoma | 46.7% | 71.2% | +24.5pp |
| 13 | Ellis, Texas | 65.3% | 89.2% | +23.9pp |
| 14 | Carter, Oklahoma | 58.3% | 81.6% | +23.4pp |
| 15 | Tippecanoe, Indiana | 48% | 70.3% | +22.3pp |
| 16 | Madera, California | 28.4% | 50.4% | +22pp |
| 17 | Wyandotte, Kansas | 39.9% | 61.9% | +22pp |
| 18 | Broward, Florida | 52.5% | 73.4% | +21pp |
| 19 | Sonoma, California | 79.2% | 100% | +20.8pp |
| 20 | San Miguel, Colorado | 62.8% | 83% | +20.3pp |
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. 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 PlainAirData 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.