# Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2025

All 38 values come from U.S. Environmental Protection Agency for 2025, so the places are comparable. 6 counties have no value for that period and are not ranked.

- Indicator id: `aqi_max`
- Unit: index
- Definition: Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: highest daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/highest-daily-air-quality-index/pennsylvania-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Chester County | 157 |
| 2 | Delaware County | 153 |
| 3 | Erie County | 149 |
| 4 | Philadelphia County | 147 |
| 5 | Warren County | 138 |
| 6 | Bucks County | 136 |
| 7 | Montgomery County | 133 |
| 8 | Beaver County | 131 |
| 9 | Allegheny County | 129 |
| 10 | Tioga County | 127 |
| 11 | Westmoreland County | 126 |
| 12 | Monroe County | 124 |
| 13 | Berks County | 122 |
| 13 | Indiana County | 122 |
| 13 | Northampton County | 122 |
| 16 | Lancaster County | 119 |
| 17 | Lackawanna County | 117 |
| 18 | Wyoming County | 116 |
| 18 | York County | 116 |
| 20 | Blair County | 115 |
| 20 | Cambria County | 115 |
| 20 | Lehigh County | 115 |
| 20 | Mercer County | 115 |
| 24 | Bradford County | 109 |
| 25 | Lebanon County | 108 |
| 26 | Susquehanna County | 107 |
| 27 | Greene County | 105 |
| 27 | Lycoming County | 105 |
| 29 | Centre County | 101 |
| 29 | Dauphin County | 101 |
| 31 | Adams County | 100 |
| 31 | Washington County | 100 |
| 33 | Armstrong County | 96 |
| 33 | Cumberland County | 96 |
| 35 | Fayette County | 93 |
| 35 | Somerset County | 93 |
| 37 | Franklin County | 87 |
| 38 | Elk County | 84 |