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)

Delaware County had the highest share of days with good air quality (US EPA AQI) of 20 counties in 2010, at 99.1%. Clinton County had the lowest, at 18.9%. The median was 58%. Source: EPA.

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Highest99.1Delaware County
Lowest18.9Clinton County
Median5820 counties

Map of counties, 2010

Black Hawk County: 44.7 %Bremer County: 87.4 %Cerro Gordo County: 95.6 %Clinton County: 18.9 %Delaware County: 99.1 %Harrison County: 84.5 %Johnson County: 23 %Lee County: 44.3 %Linn County: 39.7 %Montgomery County: 53.1 %Muscatine County: 27.7 %Palo Alto County: 59.8 %Polk County: 49.3 %Pottawattamie County: 69.2 %Scott County: 20.8 %Story County: 93.5 %Tama County: 64.3 %Van Buren County: 71.5 %Warren County: 87.4 %Woodbury County: 56.1 %
  • Under 37
  • 37 to 52
  • 52 to 66
  • 66 to 87
  • 87 and over
  • No data
%, 2010. 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, 2010

Delaware County: 99.1 %Delaware County99.1Cerro Gordo County: 95.6 %Cerro Gordo County95.6Story County: 93.5 %Story County93.5Bremer County: 87.4 %Bremer County87.4Warren County: 87.4 %Warren County87.4Harrison County: 84.5 %Harrison County84.5Van Buren County: 71.5 %Van Buren County71.5Pottawattamie County: 69.2 %Pottawattamie County69.2Tama County: 64.3 %Tama County64.3Palo Alto County: 59.8 %Palo Alto County59.8Woodbury County: 56.1 %Woodbury County56.1Montgomery County: 53.1 %Montgomery County53.1Polk County: 49.3 %Polk County49.3Black Hawk County: 44.7 %Black Hawk County44.7Lee County: 44.3 %Lee County44.3Linn County: 39.7 %Linn County39.7Muscatine County: 27.7 %Muscatine County27.7Johnson County: 23 %Johnson County23Scott County: 20.8 %Scott County20.8Clinton County: 18.9 %Clinton County18.9Delaware County: 99.1 %Delaware County99.1Cerro Gordo County: 95.6 %Cerro Gordo County95.6Story County: 93.5 %Story County93.5Bremer County: 87.4 %Bremer County87.4Warren County: 87.4 %Warren County87.4Harrison County: 84.5 %Harrison County84.5Van Buren County: 71.5 %Van Buren County71.5Pottawattamie County: 69.2 %Pottawattamie County69.2Tama County: 64.3 %Tama County64.3Palo Alto County: 59.8 %Palo Alto County59.8Woodbury County: 56.1 %Woodbury County56.1Montgomery County: 53.1 %Montgomery County53.1Polk County: 49.3 %Polk County49.3Black Hawk County: 44.7 %Black Hawk County44.7Lee County: 44.3 %Lee County44.3Linn County: 39.7 %Linn County39.7Muscatine County: 27.7 %Muscatine County27.7Johnson County: 23 %Johnson County23Scott County: 20.8 %Scott County20.8Clinton County: 18.9 %Clinton County18.9
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2010 (%)Change on 2009
1Delaware County99.1-0.9 pts
2Cerro Gordo County95.6+2.2 pts
3Story County93.5+1 pts
4Bremer County87.4-2.8 pts
4Warren County87.4-6.5 pts
6Harrison County84.5-4.3 pts
7Van Buren County71.5-3.8 pts
8Pottawattamie County69.2-7.6 pts
9Tama County64.3n/a
10Palo Alto County59.8-15.6 pts
11Woodbury County56.1-7.3 pts
12Montgomery County53.1-23.7 pts
13Polk County49.3-1.9 pts
14Black Hawk County44.7-1.6 pts
15Lee County44.3-3.2 pts
16Linn County39.7-5.8 pts
17Muscatine County27.7-10.9 pts
18Johnson County23-15.2 pts
19Scott County20.8-13.2 pts
20Clinton County18.9-13.7 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. 6 counties with data in other periods have no value for 2010 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), 2010) [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), 2010. 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=2010. 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), 2010. 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=2010.

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), 2010 [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=2010 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_iowa_by_2010,
  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), 2010}},
  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=2010. 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), 2010
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=2010
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/iowa-counties?period=2010.
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.
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Questions

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

Delaware County, with 99.1% in 2010, according to EPA.

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

Clinton County, with 18.9% in 2010.

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. 6 counties have no value for 2010 and are not ranked.

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

Counties in Iowa: more rankings