# Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 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_unhealthy_sensitive_or_worse_days_share`
- Unit: %
- Definition: Days with a daily Air Quality Index above 100 (unhealthy for sensitive groups, unhealthy, very unhealthy or hazardous) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; the counts are stored with each value.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/unhealthy-air-quality-days-share/pennsylvania-counties

| Rank | Place | % |
|---:|---|---:|
| 1 | Philadelphia County | 2.2 |
| 2 | Warren County | 2 |
| 3 | Allegheny County | 1.1 |
| 3 | Bucks County | 1.1 |
| 5 | Berks County | 0.8 |
| 5 | Delaware County | 0.8 |
| 5 | Lackawanna County | 0.8 |
| 5 | Mercer County | 0.8 |
| 5 | York County | 0.8 |
| 10 | Bradford County | 0.6 |
| 10 | Chester County | 0.6 |
| 10 | Monroe County | 0.6 |
| 10 | Susquehanna County | 0.6 |
| 10 | Wyoming County | 0.6 |
| 15 | Indiana County | 0.5 |
| 15 | Lancaster County | 0.5 |
| 15 | Lebanon County | 0.5 |
| 15 | Northampton County | 0.5 |
| 15 | Tioga County | 0.5 |
| 20 | Beaver County | 0.3 |
| 20 | Blair County | 0.3 |
| 20 | Cambria County | 0.3 |
| 20 | Centre County | 0.3 |
| 20 | Dauphin County | 0.3 |
| 20 | Erie County | 0.3 |
| 20 | Greene County | 0.3 |
| 20 | Lehigh County | 0.3 |
| 20 | Lycoming County | 0.3 |
| 20 | Montgomery County | 0.3 |
| 20 | Westmoreland County | 0.3 |
| 31 | Adams County | 0 |
| 31 | Armstrong County | 0 |
| 31 | Cumberland County | 0 |
| 31 | Elk County | 0 |
| 31 | Fayette County | 0 |
| 31 | Franklin County | 0 |
| 31 | Somerset County | 0 |
| 31 | Washington County | 0 |