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 2005, at 15.8%. Keweenaw County had the lowest, at 0%. The median was 7.9%. Source: EPA.

Highest15.8Cass County

Lowest0Keweenaw County

Median7.931 counties

Map of counties, 2005

Under 2.9
2.9 to 5.6
5.6 to 7.9
7.9 to 10
10 to 12
12 and over
No data

%, 2005. 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, 2005

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

Full ranking

Rank	Counties	2005 (%)	Change on 2004
1	Cass County	15.8	+10.5 pts
2	Berrien County	13.4	+10.9 pts
3	Lenawee County	13.2	+10.5 pts
4	Muskegon County	12.6	+11 pts
5	Benzie County	11.7	+9 pts
6	Allegan County	11.6	+7.4 pts
6	Ottawa County	11.6	+10.8 pts
8	Ingham County	10.8	+9.5 pts
9	Genesee County	10.5	+8.5 pts
10	Wayne County	10.4	+4.1 pts
11	Leelanau County	10.2	+9.1 pts
12	Clinton County	9.8	+8.2 pts
13	Macomb County	9.7	+7 pts
14	Kent County	9.3	+7.1 pts
15	St. Clair County	8.7	+5.3 pts
16	Kalamazoo County	7.9	+7.1 pts
17	Monroe County	7	+5.3 pts
18	Mason County	6.9	+4.7 pts
19	Washtenaw County	6.4	+4.4 pts
20	Oakland County	6.2	+4.6 pts
21	Huron County	5.6	+4 pts
22	Tuscola County	4.4	+3.2 pts
23	Bay County	4.3	+4.3 pts
24	Schoolcraft County	4.1	+2.4 pts
25	Saginaw County	3.5	+3.5 pts
26	Missaukee County	2.9	+1.2 pts
27	Wexford County	2.5	+1.9 pts
28	Chippewa County	0.8	+0.8 pts
29	Dickinson County	0	n/a
29	Iron County	0	n/a
29	Keweenaw 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. 22 counties with data in other periods have no value for 2005 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), 2005) [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), 2005. 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=2005. 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), 2005. 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=2005.

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), 2005 [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=2005 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_michigan_by_2005,
  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), 2005}},
  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=2005. 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), 2005
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=2005
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties?period=2005.
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  -

Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Embed code

<iframe src="https://invokely.ai/embed/rankings/unhealthy-air-quality-days-share/michigan-counties?period=2005" width="760" height="500" title="Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2005, chart from Invokely" loading="lazy" style="border:0;width:100%;max-width:760px" referrerpolicy="strict-origin-when-cross-origin"></iframe>

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Michigan by share of days unhealthy for sensitive groups or worse (US EPA AQI) using official data, and cite the source.

rank_places {"indicator":"aqi_unhealthy_sensitive_or_worse_days_share","level":"province","within":"Michigan","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_unhealthy_sensitive_or_worse_days_share&level=province&within=Michigan&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

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

Cass County, with 15.8% in 2005, according to EPA.

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

Keweenaw County, with 0% in 2005.

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 2005 and are not ranked.