State air quality · 2025
Pennsylvania Air Quality Ranking
Across 38 monitored counties, the typical county in Pennsylvania posts a median AQI of 40 (Good) and 73.8% of monitored days were rated Good, from EPA AQS.
- 40
- Avg median AQI
- 73.8%
- Good-air days
- 38
- Counties monitored
- 31%
- Cleaner than US states
Pennsylvania's typical county median AQI is 40 (Good) across 38 monitored counties
According to the U.S. EPA Air Quality System, Pennsylvania monitors 38 counties with a day-weighted Good-day share of 73.8%. Cleanest: Elk County (95.3% Good). Most polluted: Allegheny County (46.0%). These are annual summaries, not live AirNow readings.
Data source EPA Air Quality System (AQS)
- Cleaner than US states
- Pennsylvania's day-weighted Good-day share of 73.8% places it cleaner than 31% of US states.
- In-state spread
- Within Pennsylvania, Lawrence County leads at 100.0% Good days while Allegheny County sits at 46.0% across 38 monitored counties.
- 2024→2025 release
- Pennsylvania's Good-day share moved -0.5 points vs the 2024 EPA annual release.
- Typical median AQI
- Typical median AQI: 40
Verify with AirNow → · EPA AQS →
EPA state monitoring brief
AQS state key PENNSYLVANIA
Pennsylvania · 2025 EPA AQS · 38 counties · med AQI 40 · 73.8% Good · Elk→Allegheny spread
- GOOD 40 Median AQI · Good
- SHARE 73.8% Good-day share
- COUNT 38 Counties monitored
- UNH 2 Unhealthy+ days
- RANK 31% Cleaner than states
- O3 57.6% Main pollutant share
Pennsylvania's 73.8% Good-day share is cleaner than 31% of monitored US states; Elk and Allegheny County bracket the in-state range. Open Lawrence County →
According to EPA AQS annual summaries on PlainAirData, Pennsylvania ranks #36 of 52 by day-weighted good-day share (73.8%) and #30 by mean county median AQI (39.7). 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
73.8%
Good-day share in 2025, down 0.5 percentage points vs 2024. County-mean median AQI 40, within half a point of the 2024 county-mean median.
Pollutant mix
Ozone
Main driver on 57.6% of pollutant-assigned days.
- Ozone 57.6%
- PM2.5 41.8%
- NO2 0.6%
Monitoring coverage
346
Average monitored days per county in the latest release. 1 of 38 counties sit below the 100-day floor used for cleanest/most-polluted claims.
Counties Monitored
38
Good Days %
73.8%
Avg Median AQI
40
Total Unhealthy Days
2
Best Air Quality
Elk County
Worst Air Quality
Allegheny County
Where Pennsylvania sits nationally
COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Pennsylvania's day-weighted Good-day share is 73.8% - cleaner than 31% of that comparison set.
Pennsylvania Good-day share vs. every US state
Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
73.8% 31st percentile higher than 31% 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 Pennsylvania have the cleanest and most polluted air?
Cleanest counties in Pennsylvania
| County | Good % | Median AQI | Max AQI | Unhealthy Days |
|---|---|---|---|---|
| Lawrence | 100.0% | 24 | 31 | 0 |
| Elk | 95.3% | 36 | 84 | 0 |
| Somerset | 94.5% | 36 | 93 | 0 |
| Franklin | 91.5% | 37 | 87 | 0 |
| Susquehanna | 88.4% | 22 | 107 | 0 |
| Monroe | 88.3% | 36 | 124 | 0 |
| Wyoming | 86.5% | 24 | 116 | 0 |
| Bucks | 86.2% | 36 | 136 | 0 |
| Tioga | 82.1% | 39 | 127 | 0 |
| Bradford | 81.6% | 37 | 109 | 0 |
| Fayette | 78.9% | 40 | 93 | 0 |
| Warren | 78.7% | 35 | 138 | 0 |
| Westmoreland | 78.2% | 39 | 126 | 0 |
| Greene | 77.8% | 40 | 105 | 0 |
| Lycoming | 77.5% | 40 | 105 | 0 |
| Blair | 76.9% | 40 | 115 | 0 |
| Erie | 76.7% | 34 | 149 | 0 |
| Indiana | 74.8% | 39 | 122 | 0 |
| Cambria | 74.5% | 41 | 115 | 0 |
| Adams | 74.4% | 42 | 100 | 0 |
| Centre | 74.3% | 41 | 101 | 0 |
| Lackawanna | 74.0% | 39 | 117 | 0 |
| Montgomery | 73.4% | 41 | 133 | 0 |
| Mercer | 72.6% | 42 | 115 | 0 |
| Northampton | 72.0% | 38 | 122 | 0 |
| Lehigh | 72.0% | 41 | 115 | 0 |
| Cumberland | 71.5% | 35 | 96 | 0 |
| Chester | 71.3% | 43 | 157 | 1 |
| Armstrong | 70.5% | 41 | 96 | 0 |
| Berks | 68.2% | 43 | 122 | 0 |
| Washington | 67.7% | 44 | 100 | 0 |
| Delaware | 65.2% | 44 | 153 | 1 |
| Lebanon | 64.4% | 42 | 108 | 0 |
| Dauphin | 62.5% | 44 | 101 | 0 |
| Lancaster | 60.5% | 45 | 119 | 0 |
| York | 59.5% | 45 | 116 | 0 |
| Beaver | 55.6% | 46 | 131 | 0 |
| Philadelphia | 50.4% | 50 | 147 | 0 |
| Allegheny | 46.0% | 52 | 129 | 0 |
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: 38 counties in Pennsylvania 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.