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 20 counties in 2011, at 96.9%. Scott County had the lowest, at 18.1%. The median was 52.6%. Source: EPA.

Highest96.9Cerro Gordo County

Lowest18.1Scott County

Median52.620 counties

Map of counties, 2011

Under 40
40 to 49
49 to 54
54 to 82
82 and over
No data

%, 2011. 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, 2011

%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2011 (%)	Change on 2010
1	Cerro Gordo County	96.9	+1.3 pts
2	Story County	92.5	-1 pts
3	Warren County	91.6	+4.2 pts
4	Bremer County	89.7	+2.3 pts
5	Harrison County	79.8	-4.7 pts
6	Woodbury County	64	+7.9 pts
7	Montgomery County	54.7	+1.6 pts
8	Tama County	54.4	-9.9 pts
9	Van Buren County	53.7	-17.8 pts
10	Palo Alto County	53.4	-6.4 pts
11	Delaware County	51.7	-47.4 pts
12	Polk County	49.6	+0.3 pts
13	Pottawattamie County	47.1	-22.1 pts
14	Linn County	46.3	+6.6 pts
15	Lee County	41.9	-2.4 pts
16	Black Hawk County	41.6	-3.1 pts
17	Muscatine County	32.1	+4.4 pts
18	Johnson County	25.8	+2.8 pts
19	Clinton County	23.3	+4.4 pts
20	Scott County	18.1	-2.7 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 2011 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), 2011) [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), 2011. 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=2011. 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), 2011. 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=2011.

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), 2011 [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=2011 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_iowa_by_2011,
  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), 2011}},
  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=2011. 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), 2011
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=2011
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/iowa-counties?period=2011.
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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Questions

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

Cerro Gordo County, with 96.9% in 2011, according to EPA.

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

Scott County, with 18.1% in 2011.

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 2011 and are not ranked.