Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI)

Allegan County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 30 counties in 1994, at 18.8%. Van Buren County had the lowest, at 0%. The median was 5.3%. Source: EPA.

Highest18.8Allegan County

Lowest0Van Buren County

Median5.330 counties

Map of counties, 1994

Under 3.1
3.1 to 5.3
5.3 to 7.4
7.4 to 12
12 and over
No data

%, 1994. 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, 1994

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

Full ranking

Rank	Counties	1994 (%)	Change on 1993
1	Allegan County	18.8	+10.7 pts
2	Cass County	17.6	+9.4 pts
3	St. Clair County	15.8	+7.6 pts
4	Muskegon County	14.2	+4.9 pts
5	Lenawee County	14.1	+4.8 pts
6	Mason County	11.3	+0.4 pts
7	Ottawa County	11	n/a
8	Benzie County	10.9	+6.2 pts
9	Macomb County	7.9	+3.2 pts
10	Huron County	7.7	+2.6 pts
11	Berrien County	7.3	+0.7 pts
12	Wayne County	7.1	+3.8 pts
13	Kent County	6.3	+3.3 pts
14	Genesee County	6.2	+4.3 pts
15	Clinton County	5.6	+1.2 pts
16	Washtenaw County	4.9	+1.9 pts
17	Kalamazoo County	4.4	+0.6 pts
18	Oakland County	4.2	+2 pts
18	Tuscola County	4.2	+2.5 pts
20	Ingham County	3.3	-0.5 pts
21	Manistee County	2.8	+0.9 pts
22	Calhoun County	0	0 pts
22	Cheboygan County	0	0 pts
22	Gratiot County	0	0 pts
22	Marquette County	0	0 pts
22	Midland County	0	0 pts
22	Monroe County	0	-1.3 pts
22	Saginaw County	0	0 pts
22	Sanilac County	0	0 pts
22	Van Buren County	0	0 pts

Other periods

About this ranking

Days with a daily Air Quality Index above 100 (unhealthy for sensitive groups, unhealthy, very unhealthy or hazardous) 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; the counts are stored with each value.

Use the share rather than the number of days to compare counties, since the days with an AQI differ. 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. 23 counties with data in other periods have no value for 1994 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: days with an AQI above 100 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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1994) [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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1994. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties?period=1994. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1994. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties?period=1994.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1994 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties?period=1994 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_michigan_by_1994,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1994}},
  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/unhealthy-air-quality-days-share/michigan-counties?period=1994. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1994
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/unhealthy-air-quality-days-share/michigan-counties?period=1994
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties?period=1994.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 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 Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI) using official data, and cite the source.

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Questions

Which county has the highest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Allegan County, with 18.8% in 1994, according to EPA.

Which county has the lowest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Van Buren County, with 0% in 1994.

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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 23 counties have no value for 1994 and are not ranked.