State air quality · 2025
Ohio Air Quality Ranking
Across 37 monitored counties, the typical county in Ohio posts a median AQI of 43 (Good) and 67.0% of monitored days were rated Good, from EPA AQS.
- 43
- Avg median AQI
- 67.0%
- Good-air days
- 37
- Counties monitored
- 12%
- Cleaner than US states
Ohio's typical county median AQI is 43 (Good) across 37 monitored counties
According to the U.S. EPA Air Quality System, Ohio monitors 37 counties with a day-weighted Good-day share of 67.0%. Cleanest: Washington County (88.4% Good). Most polluted: Butler County (33.1%). These are annual summaries, not live AirNow readings.
Data source EPA Air Quality System (AQS)
- Cleaner than US states
- Ohio's day-weighted Good-day share of 67.0% places it cleaner than 12% of US states.
- In-state spread
- Within Ohio, Columbiana County leads at 100.0% Good days while Butler County sits at 33.1% across 37 monitored counties.
- 2024→2025 release
- Ohio's Good-day share moved -2.3 points vs the 2024 EPA annual release.
- Typical median AQI
- Typical median AQI: 43
Verify with AirNow → · EPA AQS →
EPA state monitoring brief
AQS state key OHIO
Ohio · 2025 EPA AQS · 37 counties · med AQI 43 · 67.0% Good · Washington→Butler spread
- GOOD 43 Median AQI · Good
- SHARE 67.0% Good-day share
- COUNT 37 Counties monitored
- UNH 6 Unhealthy+ days
- RANK 12% Cleaner than states
- O3 54.6% Main pollutant share
Good-day share peers
Ohio's 67.0% Good-day share is cleaner than 12% of monitored US states; Washington and Butler County bracket the in-state range. Open Columbiana County →
According to EPA AQS annual summaries on PlainAirData, Ohio ranks #45 of 52 by day-weighted good-day share (67.0%) and #45 by mean county median AQI (42.8). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).
Data updated August 2026
What changed, what drives it, and how thick is the sample
Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.
Release change
67.0%
Good-day share in 2025, down 2.3 percentage points vs 2024. County-mean median AQI 43, within half a point of the 2024 county-mean median.
Pollutant mix
Ozone
Main driver on 54.6% of pollutant-assigned days.
- Ozone 54.6%
- PM2.5 44.2%
- PM10 1.1%
- NO2 0.1%
Monitoring coverage
308
Average monitored days per county in the latest release. 1 of 37 counties sit below the 100-day floor used for cleanest/most-polluted claims.
Counties Monitored
37
Good Days %
67.0%
Avg Median AQI
43
Total Unhealthy Days
6
Best Air Quality
Washington County
Worst Air Quality
Butler County
Where Ohio sits nationally
COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Ohio's day-weighted Good-day share is 67.0% - cleaner than 12% of that comparison set.
Ohio Good-day share vs. every US state
Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
67.0% 12th percentile higher than 12% of 52 US states
Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Which counties in Ohio have the cleanest and most polluted air?
Cleanest counties in Ohio
| County | Good % | Median AQI | Max AQI | Unhealthy Days |
|---|---|---|---|---|
| Columbiana | 100.0% | 12 | 31 | 0 |
| Washington | 88.4% | 40 | 105 | 0 |
| Lorain | 87.3% | 39 | 119 | 0 |
| Noble | 85.9% | 37 | 90 | 0 |
| Licking | 85.7% | 40 | 119 | 0 |
| Greene | 85.3% | 40 | 105 | 0 |
| Knox | 85.3% | 39 | 159 | 1 |
| Wood | 85.3% | 39 | 108 | 0 |
| Delaware | 84.3% | 40 | 119 | 0 |
| Miami | 84.2% | 40 | 101 | 0 |
| Athens | 83.4% | 31 | 75 | 0 |
| Clinton | 83.1% | 41 | 112 | 0 |
| Geauga | 82.9% | 42 | 129 | 0 |
| Ashtabula | 81.2% | 43 | 122 | 0 |
| Madison | 79.1% | 43 | 112 | 0 |
| Portage | 77.5% | 43 | 150 | 0 |
| Clermont | 76.9% | 41 | 119 | 0 |
| Lawrence | 71.0% | 42 | 90 | 0 |
| Medina | 69.0% | 43 | 126 | 0 |
| Warren | 67.9% | 44 | 126 | 0 |
| Preble | 67.7% | 43 | 115 | 0 |
| Lake | 67.2% | 42 | 133 | 0 |
| Allen | 67.0% | 42 | 129 | 0 |
| Summit | 63.6% | 44 | 126 | 0 |
| Mahoning | 63.4% | 44 | 122 | 0 |
| Belmont | 63.0% | 42 | 123 | 0 |
| Clark | 61.4% | 45 | 126 | 0 |
| Montgomery | 60.3% | 46 | 129 | 0 |
| Trumbull | 60.3% | 46 | 130 | 0 |
| Scioto | 55.9% | 46 | 238 | 1 |
| Jefferson | 53.4% | 49 | 101 | 0 |
| Stark | 53.1% | 49 | 124 | 0 |
| Lucas | 47.4% | 52 | 154 | 1 |
| Cuyahoga | 43.3% | 53 | 150 | 0 |
| Franklin | 40.3% | 53 | 156 | 1 |
| Hamilton | 34.3% | 54 | 154 | 1 |
| Butler | 33.1% | 55 | 151 | 1 |
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.
Coverage: 37 counties in Ohio with active monitoring stations. Unmonitored counties are not represented.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025
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.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.