Data / Highest daily Air Quality Index (US EPA) / Jefferson County

Highest daily Air Quality Index (US EPA) in Jefferson County

Highest daily Air Quality Index (US EPA) in Jefferson County was 104 in 2008, according to the U.S. Environmental Protection Agency. That is up 36 from 2007.

2008, index104
Change on 2007+36
Series high1561990
Series low371987

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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Highest daily Air Quality Index (US EPA) in Jefferson County, 1986 to 2008

25507510012515017519861988199019921994199620081986: 58 index1987: 37 index1988: 155 index1989: 72 index1990: 156 index1991: 75 index1992: 89 index1993: 59 index1994: 69 index1995: 57 index1996: 58 index1997: 57 index2007: 68 index2008: 104 index0501001502001986199120081986: 58 index1987: 37 index1988: 155 index1989: 72 index1990: 156 index1991: 75 index1992: 89 index1993: 59 index1994: 69 index1995: 57 index1996: 58 index1997: 57 index2007: 68 index2008: 104 index
index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12, published 2026-07-13.
All 14 values
Periodindex
2008104
200768
199757
199658
199557
199469
199359
199289
199175
1990156
198972
1988155
198737
198658

Jefferson County compared with nearby places

Big Horn County: 83 indexCascade County: 71 indexFergus County: 72 indexFlathead County: 83 indexGallatin County: 85 indexJefferson County: 104 indexLake County: 84 indexLewis and Clark County: 138 indexLincoln County: 118 indexMissoula County: 104 indexPowell County: 56 indexRavalli County: 120 indexRichland County: 63 indexRoosevelt County: 69 indexRosebud County: 78 indexSanders County: 113 indexSheridan County: 82 indexSilver Bow County: 102 indexYellowstone County: 97 index
  • Under 72
  • 72 to 83
  • 83 to 95
  • 95 to 110
  • 110 and over
  • No data
Highest daily Air Quality Index (US EPA), 2008, index. Jefferson 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

Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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: highest daily AQI. 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: highest daily AQI (Highest daily Air Quality Index (US EPA), Jefferson County, 1986 to 2008) [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: highest daily AQI, Highest daily Air Quality Index (US EPA), Jefferson County, 1986 to 2008. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/en/highest-daily-air-quality-index/jefferson-county-montana. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Highest daily Air Quality Index (US EPA), Jefferson County, 1986 to 2008. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/en/highest-daily-air-quality-index/jefferson-county-montana.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Highest daily Air Quality Index (US EPA), Jefferson County, 1986 to 2008 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/en/highest-daily-air-quality-index/jefferson-county-montana (Accessed: 12 October 2026).

BibTeX
@misc{environmental_highest_daily_air_quality_2008,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Highest daily Air Quality Index (US EPA), Jefferson County, 1986 to 2008}},
  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/highest-daily-air-quality-index/jefferson-county-montana. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. 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: highest daily AQI: Highest daily Air Quality Index (US EPA), Jefferson County, 1986 to 2008
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/highest-daily-air-quality-index/jefferson-county-montana
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/highest-daily-air-quality-index/jefferson-county-montana.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

What is the highest daily Air Quality Index (US EPA) in Jefferson County?

Highest daily Air Quality Index (US EPA) in Jefferson County was 104 in 2008, according to the U.S. Environmental Protection Agency. That is up 36 from 2007.

Where does this figure come from?

U.S. Environmental Protection Agency. EPA AirData annual AQI by county: highest daily AQI. Retrieved by Invokely on 2026-10-12.

What was the highest highest daily Air Quality Index (US EPA) in Jefferson County?

156 in 1990, the highest value since 1986 in this series.

Related statistics for Jefferson County

All statistics for Jefferson County | Jefferson County in figures