County ranking · decline

Counties with the Biggest Air-Quality Decline

Where the share of Good air days fell the most between 2020 and 2025, measured as a percentage-point change so a county's monitoring schedule doesn't skew the result.

-43.1pp
Largest decline: Butler, Ohio
20
Counties ranked

This ranking measures the change in each county's share of Good air days, not the raw count. Counties shown were monitored at least 200 days in both 2020 and 2025. A decline is a descriptive arithmetic result from two EPA annual releases, it does not by itself establish a cause. See the methodology and the complementary most-improved ranking.

Largest drop in Good-day share, 2020 → 2025

Percentage-point decrease in days rated Good (AQI 0–50); bar length = magnitude

  1. 1 Butler, Ohio 43.1pp
  2. 2 Scioto, Ohio 38.9pp
  3. 3 McLennan, Texas 33.8pp
  4. 4 Kent, Michigan 31.2pp
  5. 5 Floyd, Indiana 29.8pp
  6. 6 Bibb, Georgia 28.8pp
  7. 7 Ouachita, Louisiana 27.3pp
  8. 8 Adair, Oklahoma 26pp
  9. 9 Etowah, Alabama 25.2pp
  10. 10 Bell, Kentucky 25pp
  11. 11 Brookings, South Dakota 24.7pp
  12. 12 Box Elder, Utah 24.4pp

Good-day share decline · EPA Air Quality System

# County 2020 Good % 2025 Good % Change
1 Butler, Ohio 76.2% 33.2% -43.1pp
2 Scioto, Ohio 94.8% 55.9% -38.9pp
3 McLennan, Texas 80.3% 46.6% -33.8pp
4 Kent, Michigan 73.2% 41.9% -31.2pp
5 Floyd, Indiana 95.6% 65.7% -29.8pp
6 Bibb, Georgia 71.6% 42.7% -28.8pp
7 Ouachita, Louisiana 89.5% 62.2% -27.3pp
8 Adair, Oklahoma 81.8% 55.8% -26pp
9 Etowah, Alabama 86.6% 61.4% -25.2pp
10 Bell, Kentucky 92% 67% -25pp
11 Brookings, South Dakota 83.3% 58.6% -24.7pp
12 Box Elder, Utah 89% 64.7% -24.4pp
13 Orange, Florida 96.7% 72.9% -23.8pp
14 Sedgwick, Kansas 80.9% 57.5% -23.3pp
15 Lucas, Ohio 70.6% 47.4% -23.2pp
16 Franklin, Ohio 63.4% 40.3% -23.1pp
17 Nueces, Texas 62% 40.5% -21.5pp
18 Bonner, Idaho 77.5% 56.2% -21.4pp
19 Richland, South Carolina 79% 58.1% -20.9pp
20 Montgomery, Texas 59.8% 39.1% -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 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.