Data / Share of days with good air quality (US EPA AQI) / Delta County

Share of days with good air quality (US EPA AQI) in Delta County

Share of days with good air quality (US EPA AQI) in Delta County was 96.7% in 1993, according to EPA. That is up 25.4 pts from 1992.

199396.7%
Change on 1992+25.4 pts
Series high96.71993
Series low67.31991

Next release: Tuesday, 13 July 2027, estimated by Invokely from past publication dates (low confidence), not announced by the publisher. Release calendar

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Share of days with good air quality (US EPA AQI) in Delta County, 1991 to 1993

607080901001991199219931991: 67.3 %1992: 71.3 %1993: 96.7 %607080901001991199219931991: 67.3 %1992: 71.3 %1993: 96.7 %
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12, published 2026-07-13.
All 3 values
Period%
199396.7
199271.3
199167.3

Delta County compared with nearby places

Allegan County: 69.7 %Bay County: 96.6 %Benzie County: 81.9 %Berrien County: 70.3 %Calhoun County: 96.7 %Cass County: 65.6 %Cheboygan County: 100 %Clinton County: 81.8 %Delta County: 96.7 %Dickinson County: 92.8 %Genesee County: 81.7 %Gratiot County: 100 %Huron County: 81.8 %Ingham County: 84.2 %Kalamazoo County: 80.5 %Kent County: 86.8 %Lenawee County: 68.6 %Macomb County: 87.4 %Manistee County: 90.9 %Marquette County: 98.4 %Mason County: 69.8 %Midland County: 97.8 %Monroe County: 84.4 %Muskegon County: 75.3 %Oakland County: 90.8 %Saginaw County: 98.4 %St. Clair County: 73.8 %Sanilac County: 100 %Tuscola County: 91.5 %Van Buren County: 100 %Washtenaw County: 85.7 %Wayne County: 63.6 %
  • Under 71
  • 71 to 82
  • 82 to 86
  • 86 to 92
  • 92 to 98
  • 98 and over
  • No data
Share of days with good air quality (US EPA AQI), 1993, %. Delta County is outlined. Same source and period for every area shown. Source: U.S. Environmental Protection Agency. Boundaries: U.S. Census Bureau cartographic boundary files.

Rankings

Definition

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.

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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 (Share of days with good air quality (US EPA AQI), Delta County, 1991 to 1993) [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, Share of days with good air quality (US EPA AQI), Delta County, 1991 to 1993. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/en/good-air-quality-days-share/delta-county-michigan. 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. Share of days with good air quality (US EPA AQI), Delta County, 1991 to 1993. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/en/good-air-quality-days-share/delta-county-michigan.

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, Share of days with good air quality (US EPA AQI), Delta County, 1991 to 1993 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/en/good-air-quality-days-share/delta-county-michigan (Accessed: 12 October 2026).

BibTeX
@misc{environmental_share_of_days_with_1993,
  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: Share of days with good air quality (US EPA AQI), Delta County, 1991 to 1993}},
  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/en/good-air-quality-days-share/delta-county-michigan. 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: Share of days with good air quality (US EPA AQI), Delta County, 1991 to 1993
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/en/good-air-quality-days-share/delta-county-michigan
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/good-air-quality-days-share/delta-county-michigan.
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

What is the share of days with good air quality (US EPA AQI) in Delta County?

Share of days with good air quality (US EPA AQI) in Delta County was 96.7% in 1993, according to EPA. That is up 25.4 pts from 1992.

Where does this figure come from?

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 by Invokely on 2026-10-12.

What was the highest share of days with good air quality (US EPA AQI) in Delta County?

96.7% in 1993, the highest value since 1991 in this series.

Related statistics for Delta County

All statistics for Delta County | Delta County in figures