Data / Rankings / Median Air Quality Index (US EPA) / Counties in Pennsylvania

Counties in Pennsylvania by median Air Quality Index (US EPA)

Allegheny County had the highest median Air Quality Index (US EPA) of 40 counties in 2021, at 57. Lawrence County had the lowest, at 31. The median was 45. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest57Allegheny County
Lowest31Lawrence County
Median4540 counties

Map of counties, 2021

Adams County: 47 indexAllegheny County: 57 indexArmstrong County: 48 indexBeaver County: 52 indexBerks County: 48 indexBlair County: 45 indexBradford County: 42 indexBucks County: 37 indexCambria County: 51 indexCentre County: 43 indexChester County: 45 indexClearfield County: 33 indexCumberland County: 47 indexDauphin County: 52 indexDelaware County: 51 indexElk County: 34 indexErie County: 38 indexFayette County: 43 indexFranklin County: 35 indexGreene County: 42 indexIndiana County: 44 indexLackawanna County: 40 indexLancaster County: 56 indexLawrence County: 31 indexLebanon County: 49 indexLehigh County: 47 indexLuzerne County: 34 indexLycoming County: 44 indexMercer County: 40 indexMonroe County: 35 indexMontgomery County: 47 indexNorthampton County: 45 indexPhiladelphia County: 54 indexSomerset County: 34 indexSusquehanna County: 35 indexTioga County: 38 indexWashington County: 49 indexWestmoreland County: 47 indexWyoming County: 34 indexYork County: 51 index
  • Under 35
  • 35 to 40
  • 40 to 45
  • 45 to 47
  • 47 to 51
  • 51 and over
  • No data
index, 2021. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2021

Allegheny County: 57 indexAllegheny County57Lancaster County: 56 indexLancaster County56Philadelphia County: 54 indexPhiladelphia County54Beaver County: 52 indexBeaver County52Dauphin County: 52 indexDauphin County52Cambria County: 51 indexCambria County51Delaware County: 51 indexDelaware County51York County: 51 indexYork County51Lebanon County: 49 indexLebanon County49Washington County: 49 indexWashington County49Armstrong County: 48 indexArmstrong County48Berks County: 48 indexBerks County48Adams County: 47 indexAdams County47Cumberland County: 47 indexCumberland County47Lehigh County: 47 indexLehigh County47Montgomery County: 47 indexMontgomery County47Westmoreland County: 47 indexWestmoreland County47Blair County: 45 indexBlair County45Chester County: 45 indexChester County45Northampton County: 45 indexNorthampton County45Indiana County: 44 indexIndiana County44Lycoming County: 44 indexLycoming County44Centre County: 43 indexCentre County43Fayette County: 43 indexFayette County43Bradford County: 42 indexBradford County42Greene County: 42 indexGreene County42Lackawanna County: 40 indexLackawanna County40Mercer County: 40 indexMercer County40Erie County: 38 indexErie County38Tioga County: 38 indexTioga County38Bucks County: 37 indexBucks County37Franklin County: 35 indexFranklin County35Monroe County: 35 indexMonroe County35Susquehanna County: 35 indexSusquehanna County35Elk County: 34 indexElk County34Luzerne County: 34 indexLuzerne County34Somerset County: 34 indexSomerset County34Wyoming County: 34 indexWyoming County34Clearfield County: 33 indexClearfield County33Lawrence County: 31 indexLawrence County31Allegheny County: 57 indexAllegheny County57Lancaster County: 56 indexLancaster County56Philadelphia County: 54 indexPhiladelphia County54Beaver County: 52 indexBeaver County52Dauphin County: 52 indexDauphin County52Cambria County: 51 indexCambria County51Delaware County: 51 indexDelaware County51York County: 51 indexYork County51Lebanon County: 49 indexLebanon County49Washington County: 49 indexWashington County49Armstrong County: 48 indexArmstrong County48Berks County: 48 indexBerks County48Adams County: 47 indexAdams County47Cumberland County: 47 indexCumberland County47Lehigh County: 47 indexLehigh County47Montgomery County: 47 indexMontgomery County47Westmoreland County: 47 indexWestmoreland County47Blair County: 45 indexBlair County45Chester County: 45 indexChester County45Northampton County: 45 indexNorthampton County45Indiana County: 44 indexIndiana County44Lycoming County: 44 indexLycoming County44Centre County: 43 indexCentre County43Fayette County: 43 indexFayette County43Bradford County: 42 indexBradford County42Greene County: 42 indexGreene County42Lackawanna County: 40 indexLackawanna County40Mercer County: 40 indexMercer County40Erie County: 38 indexErie County38Tioga County: 38 indexTioga County38Bucks County: 37 indexBucks County37Franklin County: 35 indexFranklin County35Monroe County: 35 indexMonroe County35Susquehanna County: 35 indexSusquehanna County35Elk County: 34 indexElk County34Luzerne County: 34 indexLuzerne County34Somerset County: 34 indexSomerset County34Wyoming County: 34 indexWyoming County34Clearfield County: 33 indexClearfield County33Lawrence County: 31 indexLawrence County31
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2021
index		Change on 2020
1Allegheny County57+3
2Lancaster County56+5
3Philadelphia County54+7
4Beaver County52+4
4Dauphin County52+6
6Cambria County51+7
6Delaware County51-1
6York County51+5
9Lebanon County49+8
9Washington County49+3
11Armstrong County48+5
11Berks County48+4
13Adams County47+5
13Cumberland County47+3
13Lehigh County47+6
13Montgomery County47+4
13Westmoreland County47+8
18Blair County45+2
18Chester County45+1
18Northampton County45+4
21Indiana County44+7
21Lycoming County44+3
23Centre County43+2
23Fayette County43+1
25Bradford County42+3
25Greene County42+3
27Lackawanna County400
27Mercer County40-1
29Erie County38+2
29Tioga County38-1
31Bucks County37+4
32Franklin County35+3
32Monroe County35+2
32Susquehanna County35+4
35Elk County340
35Luzerne County34+3
35Somerset County340
35Wyoming County34+1
39Clearfield County33+2
40Lawrence County310

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 4 counties with data in other periods have no value for 2021 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: median daily AQI (Counties in Pennsylvania by median Air Quality Index (US EPA), 2021) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: median daily AQI, Counties in Pennsylvania by median Air Quality Index (US EPA), 2021. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/pennsylvania-counties?period=2021. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Pennsylvania by median Air Quality Index (US EPA), 2021. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/pennsylvania-counties?period=2021.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Pennsylvania by median Air Quality Index (US EPA), 2021 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/pennsylvania-counties?period=2021 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_pennsylvania_by_2021,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Pennsylvania by median Air Quality Index (US EPA), 2021}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/pennsylvania-counties?period=2021. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: median daily AQI: Counties in Pennsylvania by median Air Quality Index (US EPA), 2021
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/median-air-quality-index/pennsylvania-counties?period=2021
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/pennsylvania-counties?period=2021.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Rank Counties in Pennsylvania by median Air Quality Index (US EPA) using official data, and cite the source.
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Questions

Which county has the highest median Air Quality Index (US EPA)?

Allegheny County, with 57 in 2021, according to the U.S. Environmental Protection Agency.

Which county has the lowest median Air Quality Index (US EPA)?

Lawrence County, with 31 in 2021.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12. 4 counties have no value for 2021 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Pennsylvania: more rankings