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

Allegheny County had the highest highest daily Air Quality Index (US EPA) of 37 counties in 2017, at 168. Franklin County had the lowest, at 67. The median was 100. Source: the U.S. Environmental Protection Agency.

Highest168Allegheny County

Lowest67Franklin County

Median10037 counties

Map of counties, 2017

Under 89
89 to 93
93 to 100
100 to 120
120 to 130
130 and over
No data

index, 2017. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2017

index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2017 index	Change on 2016
1	Allegheny County	168	+16
2	Philadelphia County	166	+19
3	Bucks County	143	-4
4	Chester County	136	-7
5	Adams County	129	+10
5	Montgomery County	129	-11
7	Lancaster County	128	-8
8	Lebanon County	127	+5
9	Berks County	122	-7
9	Erie County	122	-7
11	Delaware County	119	-17
11	Northampton County	119	-123
13	Lehigh County	115	-14
14	Dauphin County	110	-5
15	Mercer County	108	-35
16	Beaver County	105	-21
17	Cumberland County	103	-13
18	Centre County	100	-22
18	Indiana County	100	-36
18	Monroe County	100	-40
18	Westmoreland County	100	-12
22	Somerset County	97	-8
23	Armstrong County	93	-26
23	Greene County	93	-12
23	York County	93	-40
26	Cambria County	92	-5
27	Lackawanna County	91	-38
28	Elk County	90	-36
28	Lawrence County	90	-22
28	Washington County	90	-39
31	Blair County	89	-33
32	Clearfield County	84	-35
32	Lycoming County	84	-24
32	Tioga County	84	-28
35	Bradford County	77	-20
36	Luzerne County	71	-48
37	Franklin County	67	-7

Other periods

About this ranking

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.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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 2017 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: highest 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: highest daily AQI (Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2017) [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: highest daily AQI, Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2017. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/pennsylvania-counties?period=2017. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2017. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/pennsylvania-counties?period=2017.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2017 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/highest-daily-air-quality-index/pennsylvania-counties?period=2017 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_pennsylvania_by_2017,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2017}},
  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/highest-daily-air-quality-index/pennsylvania-counties?period=2017. Publisher attribution: 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.},
}

RIS

TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: highest daily AQI: Counties in Pennsylvania by highest daily Air Quality Index (US EPA), 2017
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/highest-daily-air-quality-index/pennsylvania-counties?period=2017
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/pennsylvania-counties?period=2017.
N1  - Publisher attribution: 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.
ER  -

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Rank Counties in Pennsylvania by highest daily Air Quality Index (US EPA) using official data, and cite the source.

rank_places {"indicator":"aqi_max","level":"province","within":"Pennsylvania","limit":10}
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Questions

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

Allegheny County, with 168 in 2017, according to the U.S. Environmental Protection Agency.

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

Franklin County, with 67 in 2017.

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: highest daily AQI. Retrieved 2026-10-12. 7 counties have no value for 2017 and are not ranked.