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

Cass County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 31 counties in 1992, at 12.3%. Sanilac County had the lowest, at 0%. The median was 3.6%. Source: EPA.

Highest12.3Cass County

Lowest0Sanilac County

Median3.631 counties

Map of counties, 1992

Under 0.8
0.8 to 3.6
3.6 to 4.4
4.4 to 6.3
6.3 and over
No data

%, 1992. 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, 1992

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

Full ranking

Rank	Counties	1992 (%)	Change on 1991
1	Cass County	12.3	-26.2 pts
2	Ottawa County	10.3	-11.2 pts
3	Muskegon County	8.8	-12.3 pts
4	Delta County	8.2	-7.7 pts
5	Clinton County	6.6	-6.5 pts
6	Benzie County	6.3	-15.9 pts
7	St. Clair County	5.5	-13.2 pts
8	Berrien County	5.4	-29.1 pts
9	Ingham County	4.9	-5.8 pts
10	Washtenaw County	4.7	-5 pts
11	Manistee County	4.4	-4 pts
12	Kalamazoo County	4.1	+2.8 pts
13	Tuscola County	3.9	-4.5 pts
14	Genesee County	3.8	-9.3 pts
14	Macomb County	3.8	-6.9 pts
16	Kent County	3.6	-7.4 pts
16	Wayne County	3.6	-8.7 pts
18	Oakland County	2.5	-6 pts
19	Dickinson County	2.2	+0.3 pts
19	Van Buren County	2.2	-3.1 pts
21	Bay County	0.8	+0.8 pts
22	Allegan County	0	-40.2 pts
22	Calhoun County	0	0 pts
22	Cheboygan County	0	n/a
22	Gratiot County	0	0 pts
22	Marquette County	0	0 pts
22	Mason County	0	-18.9 pts
22	Midland County	0	0 pts
22	Monroe County	0	0 pts
22	Saginaw County	0	0 pts
22	Sanilac County	0	n/a

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. 22 counties with data in other periods have no value for 1992 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), 1992) [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), 1992. 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=1992. 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), 1992. 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=1992.

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), 1992 [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=1992 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_michigan_by_1992,
  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), 1992}},
  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=1992. 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), 1992
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=1992
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties?period=1992.
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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Questions

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

Cass County, with 12.3% in 1992, according to EPA.

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

Sanilac County, with 0% in 1992.

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. 22 counties have no value for 1992 and are not ranked.