Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Iowa

Counties in Iowa by share of days with good air quality (US EPA AQI)

Cerro Gordo County had the highest share of days with good air quality (US EPA AQI) of 19 counties in 2015, at 98.6%. Scott County had the lowest, at 17.8%. The median was 66.4%. Source: EPA.

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Highest98.6Cerro Gordo County
Lowest17.8Scott County
Median66.419 counties

Map of counties, 2015

Black Hawk County: 23.2 %Bremer County: 93.5 %Cerro Gordo County: 98.6 %Clinton County: 31.2 %Delaware County: 67.8 %Harrison County: 89.3 %Johnson County: 54.2 %Lee County: 68.6 %Linn County: 53.4 %Montgomery County: 63.3 %Muscatine County: 50.1 %Palo Alto County: 52.1 %Polk County: 69 %Pottawattamie County: 66.4 %Scott County: 17.8 %Story County: 94.8 %Van Buren County: 59.5 %Warren County: 95.3 %Woodbury County: 74.4 %
  • Under 51
  • 51 to 60
  • 60 to 68
  • 68 to 91
  • 91 and over
  • No data
%, 2015. 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, 2015

Cerro Gordo County: 98.6 %Cerro Gordo County98.6Warren County: 95.3 %Warren County95.3Story County: 94.8 %Story County94.8Bremer County: 93.5 %Bremer County93.5Harrison County: 89.3 %Harrison County89.3Woodbury County: 74.4 %Woodbury County74.4Polk County: 69 %Polk County69Lee County: 68.6 %Lee County68.6Delaware County: 67.8 %Delaware County67.8Pottawattamie County: 66.4 %Pottawattamie County66.4Montgomery County: 63.3 %Montgomery County63.3Van Buren County: 59.5 %Van Buren County59.5Johnson County: 54.2 %Johnson County54.2Linn County: 53.4 %Linn County53.4Palo Alto County: 52.1 %Palo Alto County52.1Muscatine County: 50.1 %Muscatine County50.1Clinton County: 31.2 %Clinton County31.2Black Hawk County: 23.2 %Black Hawk County23.2Scott County: 17.8 %Scott County17.8Cerro Gordo County: 98.6 %Cerro Gordo County98.6Warren County: 95.3 %Warren County95.3Story County: 94.8 %Story County94.8Bremer County: 93.5 %Bremer County93.5Harrison County: 89.3 %Harrison County89.3Woodbury County: 74.4 %Woodbury County74.4Polk County: 69 %Polk County69Lee County: 68.6 %Lee County68.6Delaware County: 67.8 %Delaware County67.8Pottawattamie County: 66.4 %Pottawattamie County66.4Montgomery County: 63.3 %Montgomery County63.3Van Buren County: 59.5 %Van Buren County59.5Johnson County: 54.2 %Johnson County54.2Linn County: 53.4 %Linn County53.4Palo Alto County: 52.1 %Palo Alto County52.1Muscatine County: 50.1 %Muscatine County50.1Clinton County: 31.2 %Clinton County31.2Black Hawk County: 23.2 %Black Hawk County23.2Scott County: 17.8 %Scott County17.8
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2015 (%)Change on 2014
1Cerro Gordo County98.6-0.8 pts
2Warren County95.3+1.9 pts
3Story County94.8+6 pts
4Bremer County93.5+1.5 pts
5Harrison County89.3+1.6 pts
6Woodbury County74.4+6.1 pts
7Polk County69+6.8 pts
8Lee County68.6+17.4 pts
9Delaware County67.8+7.5 pts
10Pottawattamie County66.4+6.7 pts
11Montgomery County63.3+9.5 pts
12Van Buren County59.5+10.1 pts
13Johnson County54.2-1 pts
14Linn County53.4+2.2 pts
15Palo Alto County52.1-0.7 pts
16Muscatine County50.1+7.1 pts
17Clinton County31.2+1.3 pts
18Black Hawk County23.2-1.8 pts
19Scott County17.8+5.5 pts

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) 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; both counts are stored with each value.

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: good days 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: good days as a share of days with an AQI, calculated with stored counts (Counties in Iowa by share of days with good air quality (US EPA AQI), 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: good days as a share of days with an AQI, calculated with stored counts, Counties in Iowa by share of days with good air quality (US EPA AQI), 2015. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/iowa-counties?period=2015. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Counties in Iowa by share of days with good air quality (US EPA AQI), 2015. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/iowa-counties?period=2015.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Iowa by share of days with good air quality (US EPA AQI), 2015 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/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: good days as a share of days with an AQI, calculated with stored counts: Counties in Iowa by share of days with good air quality (US EPA AQI), 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/good-air-quality-days-share/iowa-counties?period=2015. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days 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: good days as a share of days with an AQI, calculated with stored counts: Counties in Iowa by share of days with good air quality (US EPA AQI), 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/good-air-quality-days-share/iowa-counties?period=2015
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/iowa-counties?period=2015.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days 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 Iowa by share of days with good air quality (US EPA AQI) using official data, and cite the source.
rank_places {"indicator":"aqi_good_days_share","level":"province","within":"Iowa","limit":10}
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Questions

Which county has the highest share of days with good air quality (US EPA AQI)?

Cerro Gordo County, with 98.6% in 2015, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Scott County, with 17.8% 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: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 7 counties have no value for 2015 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Iowa: more rankings