Data / Rankings / Share of days unhealthy for sensitive groups or worse (US EPA AQI) / Counties in Pennsylvania

Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI)

Allegheny County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 37 counties in 2016, at 5.5%. Franklin County had the lowest, at 0%. The median was 1.1%. Source: EPA.

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Highest5.5Allegheny County
Lowest0Franklin County
Median1.137 counties

Map of counties, 2016

Adams County: 1.4 %Allegheny County: 5.5 %Armstrong County: 1.4 %Beaver County: 1.1 %Berks County: 1.9 %Blair County: 0.5 %Bradford County: 0 %Bucks County: 2.6 %Cambria County: 0 %Centre County: 0.5 %Chester County: 2.5 %Clearfield County: 0.3 %Cumberland County: 0.3 %Dauphin County: 1.6 %Delaware County: 1.4 %Elk County: 0.9 %Erie County: 0.5 %Franklin County: 0 %Greene County: 0.3 %Indiana County: 1.1 %Lackawanna County: 1.1 %Lancaster County: 1.6 %Lawrence County: 0.3 %Lebanon County: 1.9 %Lehigh County: 1.6 %Luzerne County: 0.3 %Lycoming County: 0.3 %Mercer County: 0.8 %Monroe County: 0.8 %Montgomery County: 1.6 %Northampton County: 2.7 %Philadelphia County: 2.5 %Somerset County: 0.3 %Tioga County: 0.5 %Washington County: 0.8 %Westmoreland County: 1.4 %York County: 1.4 %
  • Under 0.3
  • 0.3 to 0.5
  • 0.5 to 1.1
  • 1.1 to 1.4
  • 1.4 to 1.9
  • 1.9 and over
  • No data
%, 2016. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2016

Allegheny County: 5.5 %Allegheny County5.5Northampton County: 2.7 %Northampton County2.7Bucks County: 2.6 %Bucks County2.6Chester County: 2.5 %Chester County2.5Philadelphia County: 2.5 %Philadelphia County2.5Berks County: 1.9 %Berks County1.9Lebanon County: 1.9 %Lebanon County1.9Dauphin County: 1.6 %Dauphin County1.6Lancaster County: 1.6 %Lancaster County1.6Lehigh County: 1.6 %Lehigh County1.6Montgomery County: 1.6 %Montgomery County1.6Adams County: 1.4 %Adams County1.4Armstrong County: 1.4 %Armstrong County1.4Delaware County: 1.4 %Delaware County1.4Westmoreland County: 1.4 %Westmoreland County1.4York County: 1.4 %York County1.4Beaver County: 1.1 %Beaver County1.1Indiana County: 1.1 %Indiana County1.1Lackawanna County: 1.1 %Lackawanna County1.1Elk County: 0.9 %Elk County0.9Mercer County: 0.8 %Mercer County0.8Monroe County: 0.8 %Monroe County0.8Washington County: 0.8 %Washington County0.8Blair County: 0.5 %Blair County0.5Centre County: 0.5 %Centre County0.5Erie County: 0.5 %Erie County0.5Tioga County: 0.5 %Tioga County0.5Clearfield County: 0.3 %Clearfield County0.3Cumberland County: 0.3 %Cumberland County0.3Greene County: 0.3 %Greene County0.3Lawrence County: 0.3 %Lawrence County0.3Luzerne County: 0.3 %Luzerne County0.3Lycoming County: 0.3 %Lycoming County0.3Somerset County: 0.3 %Somerset County0.3Bradford County: 0 %Bradford County0Cambria County: 0 %Cambria County0Franklin County: 0 %Franklin County0Allegheny County: 5.5 %Allegheny County5.5Northampton County: 2.7 %Northampton County2.7Bucks County: 2.6 %Bucks County2.6Chester County: 2.5 %Chester County2.5Philadelphia County: 2.5 %Philadelphia County2.5Berks County: 1.9 %Berks County1.9Lebanon County: 1.9 %Lebanon County1.9Dauphin County: 1.6 %Dauphin County1.6Lancaster County: 1.6 %Lancaster County1.6Lehigh County: 1.6 %Lehigh County1.6Montgomery County: 1.6 %Montgomery County1.6Adams County: 1.4 %Adams County1.4Armstrong County: 1.4 %Armstrong County1.4Delaware County: 1.4 %Delaware County1.4Westmoreland County: 1.4 %Westmoreland County1.4York County: 1.4 %York County1.4Beaver County: 1.1 %Beaver County1.1Indiana County: 1.1 %Indiana County1.1Lackawanna County: 1.1 %Lackawanna County1.1Elk County: 0.9 %Elk County0.9Mercer County: 0.8 %Mercer County0.8Monroe County: 0.8 %Monroe County0.8Washington County: 0.8 %Washington County0.8Blair County: 0.5 %Blair County0.5Centre County: 0.5 %Centre County0.5Erie County: 0.5 %Erie County0.5Tioga County: 0.5 %Tioga County0.5Clearfield County: 0.3 %Clearfield County0.3Cumberland County: 0.3 %Cumberland County0.3Greene County: 0.3 %Greene County0.3Lawrence County: 0.3 %Lawrence County0.3Luzerne County: 0.3 %Luzerne County0.3Lycoming County: 0.3 %Lycoming County0.3Somerset County: 0.3 %Somerset County0.3Bradford County: 0 %Bradford County0Cambria County: 0 %Cambria County0Franklin County: 0 %Franklin County0
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2016 (%)Change on 2015
1Allegheny County5.5+0.3 pts
2Northampton County2.7+1.3 pts
3Bucks County2.6-2.1 pts
4Chester County2.5+2 pts
4Philadelphia County2.5-1.9 pts
6Berks County1.9+0.3 pts
6Lebanon County1.9-1.4 pts
8Dauphin County1.6-0.6 pts
8Lancaster County1.6-1.1 pts
8Lehigh County1.6+0.8 pts
8Montgomery County1.60 pts
12Adams County1.4+1.1 pts
12Armstrong County1.4+0.6 pts
12Delaware County1.4-1.1 pts
12Westmoreland County1.4+0.6 pts
12York County1.4-1.1 pts
17Beaver County1.1-0.3 pts
17Indiana County1.10 pts
17Lackawanna County1.1+0.3 pts
20Elk County0.9+0.6 pts
21Mercer County0.80 pts
21Monroe County0.8+0.5 pts
21Washington County0.8-1.1 pts
24Blair County0.50 pts
24Centre County0.50 pts
24Erie County0.50 pts
24Tioga County0.5+0.5 pts
28Clearfield County0.3+0.3 pts
28Cumberland County0.30 pts
28Greene County0.3-0.8 pts
28Lawrence County0.30 pts
28Luzerne County0.30 pts
28Lycoming County0.3+0.3 pts
28Somerset County0.3+0.3 pts
35Bradford County00 pts
35Cambria County00 pts
35Franklin County00 pts

Other periods

About this ranking

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.

Use the share rather than the number of days to compare counties, since the days with an AQI differ. 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. 7 counties with data in other periods have no value for 2016 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: 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 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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2016) [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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2016. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/pennsylvania-counties?period=2016. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2016. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/pennsylvania-counties?period=2016.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2016 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/unhealthy-air-quality-days-share/pennsylvania-counties?period=2016 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_pennsylvania_by_2016,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2016}},
  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/unhealthy-air-quality-days-share/pennsylvania-counties?period=2016. Publisher attribution: 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.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2016
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/unhealthy-air-quality-days-share/pennsylvania-counties?period=2016
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/pennsylvania-counties?period=2016.
N1  - Publisher attribution: 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.
ER  -
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Rank Counties in Pennsylvania by share of days unhealthy for sensitive groups or worse (US EPA AQI) using official data, and cite the source.
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Questions

Which county has the highest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Allegheny County, with 5.5% in 2016, according to EPA.

Which county has the lowest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Franklin County, with 0% in 2016.

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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 7 counties have no value for 2016 and are not ranked.

Share of days unhealthy for sensitive groups or worse (US EPA AQI): other rankings

Counties in Pennsylvania: more rankings