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Air quality in Pennsylvania

EPA monitors report from 41 of Pennsylvania’s 67 counties. That is the honest limit of this page: the other 26 are not measured, not clean. In 2025 the most affected monitored county was Philadelphia County, with 8 days above the moderate category.

41
Counties with monitors
26
Counties without
65
Days above moderate, 2025
Summed across monitored counties
10.6%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Pennsylvania counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2025 days by category
Philadelphia County738147
Allegheny County784129
Bucks County614136
Berks County653122
Delaware County653153
Lackawanna County603117
Mercer County643115
Warren County583138
York County673116
Bradford County542109
Chester County642157
Indiana County592122
Lancaster County712119
Lebanon County652108
Monroe County522124
Northampton County642122
Susquehanna County512107
Tioga County562127
Wyoming County532116
Beaver County711131
Blair County601115
Cambria County581115
Centre County581101
Dauphin County651101
Erie County591149
Greene County611105
Lehigh County631115
Lycoming County611105
Montgomery County611133
Westmoreland County581126
Adams County610100
Armstrong County61096
Clearfield County44097
Cumberland County62096
Elk County47084
Fayette County59093
Franklin County49087
Lawrence County29031
Luzerne County47074
Somerset County46093
Washington County620100

EPA Air Quality System annual summaries by county, 2025. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.

Not measured

26 counties without a monitor

No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.

Other states

Air quality elsewhere