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

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

Scott County had the highest median Air Quality Index (US EPA) of 19 counties in 2015, at 61. Cerro Gordo County had the lowest, at 16. The median was 44. Source: the U.S. Environmental Protection Agency.

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Highest61Scott County
Lowest16Cerro Gordo County
Median4419 counties

Map of counties, 2015

Black Hawk County: 56 indexBremer County: 36 indexCerro Gordo County: 16 indexClinton County: 56 indexDelaware County: 38 indexHarrison County: 40 indexJohnson County: 48 indexLee County: 44 indexLinn County: 48 indexMontgomery County: 44 indexMuscatine County: 50 indexPalo Alto County: 50 indexPolk County: 44 indexPottawattamie County: 43 indexScott County: 61 indexStory County: 36 indexVan Buren County: 47 indexWarren County: 35 indexWoodbury County: 38 index
  • Under 37
  • 37 to 43
  • 43 to 46
  • 46 to 50
  • 50 and over
  • No data
index, 2015. 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, 2015

Scott County: 61 indexScott County61Black Hawk County: 56 indexBlack Hawk County56Clinton County: 56 indexClinton County56Muscatine County: 50 indexMuscatine County50Palo Alto County: 50 indexPalo Alto County50Johnson County: 48 indexJohnson County48Linn County: 48 indexLinn County48Van Buren County: 47 indexVan Buren County47Lee County: 44 indexLee County44Montgomery County: 44 indexMontgomery County44Polk County: 44 indexPolk County44Pottawattamie County: 43 indexPottawattamie County43Harrison County: 40 indexHarrison County40Delaware County: 38 indexDelaware County38Woodbury County: 38 indexWoodbury County38Bremer County: 36 indexBremer County36Story County: 36 indexStory County36Warren County: 35 indexWarren County35Cerro Gordo County: 16 indexCerro Gordo County16Scott County: 61 indexScott County61Black Hawk County: 56 indexBlack Hawk County56Clinton County: 56 indexClinton County56Muscatine County: 50 indexMuscatine County50Palo Alto County: 50 indexPalo Alto County50Johnson County: 48 indexJohnson County48Linn County: 48 indexLinn County48Van Buren County: 47 indexVan Buren County47Lee County: 44 indexLee County44Montgomery County: 44 indexMontgomery County44Polk County: 44 indexPolk County44Pottawattamie County: 43 indexPottawattamie County43Harrison County: 40 indexHarrison County40Delaware County: 38 indexDelaware County38Woodbury County: 38 indexWoodbury County38Bremer County: 36 indexBremer County36Story County: 36 indexStory County36Warren County: 35 indexWarren County35Cerro Gordo County: 16 indexCerro Gordo County16
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2015
index		Change on 2014
1Scott County61+2
2Black Hawk County560
2Clinton County560
4Muscatine County50-3
4Palo Alto County500
6Johnson County48+1
6Linn County48-2
8Van Buren County47-4
9Lee County44-4
9Montgomery County44-4
9Polk County440
12Pottawattamie County43-3
13Harrison County40+2
14Delaware County38-5
14Woodbury County38-1
16Bremer County36-1
16Story County36-1
18Warren County350
19Cerro Gordo County160

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. 7 counties with data in other periods have no value for 2015 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 Iowa by median Air Quality Index (US EPA), 2015) [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 Iowa by median Air Quality Index (US EPA), 2015. 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/iowa-counties?period=2015. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Iowa by median Air Quality Index (US EPA), 2015. 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/iowa-counties?period=2015.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Iowa by median Air Quality Index (US EPA), 2015 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/iowa-counties?period=2015 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_iowa_by_2015,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Iowa by median Air Quality Index (US EPA), 2015}},
  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/iowa-counties?period=2015. 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 Iowa by median Air Quality Index (US EPA), 2015
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/iowa-counties?period=2015
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/iowa-counties?period=2015.
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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Questions

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

Scott County, with 61 in 2015, according to the U.S. Environmental Protection Agency.

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

Cerro Gordo County, with 16 in 2015.

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. 7 counties have no value for 2015 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Iowa: more rankings