Data / Rankings / Share of days unhealthy for sensitive groups or worse (US EPA AQI) / Counties in Utah

Counties in Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025

Salt Lake County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 17 counties in 2025, at 4.4%. Wayne County had the lowest, at 0%. The median was 0.3%. Source: EPA.

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Highest4.4Salt Lake County
Lowest0Wayne County
Median0.317 counties

Map of counties, 2025

Box Elder County: 0.3 %Cache County: 0 %Carbon County: 0.5 %Davis County: 1.9 %Duchesne County: 0.5 %Garfield County: 0 %Grand County: 0 %Iron County: 0.3 %Salt Lake County: 4.4 %San Juan County: 0.3 %Tooele County: 0.3 %Uintah County: 1.1 %Utah County: 0.3 %Wasatch County: 0.3 %Washington County: 0 %Wayne County: 0 %Weber County: 0.5 %
  • Under 0.3
  • 0.3 to 0.5
  • 0.5 and over
  • No data
%, 2025. 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, 2025

Salt Lake County: 4.4 %Salt Lake County4.4Davis County: 1.9 %Davis County1.9Uintah County: 1.1 %Uintah County1.1Carbon County: 0.5 %Carbon County0.5Duchesne County: 0.5 %Duchesne County0.5Weber County: 0.5 %Weber County0.5Box Elder County: 0.3 %Box Elder County0.3Iron County: 0.3 %Iron County0.3San Juan County: 0.3 %San Juan County0.3Tooele County: 0.3 %Tooele County0.3Utah County: 0.3 %Utah County0.3Wasatch County: 0.3 %Wasatch County0.3Cache County: 0 %Cache County0Garfield County: 0 %Garfield County0Grand County: 0 %Grand County0Washington County: 0 %Washington County0Wayne County: 0 %Wayne County0Salt Lake County: 4.4 %Salt Lake County4.4Davis County: 1.9 %Davis County1.9Uintah County: 1.1 %Uintah County1.1Carbon County: 0.5 %Carbon County0.5Duchesne County: 0.5 %Duchesne County0.5Weber County: 0.5 %Weber County0.5Box Elder County: 0.3 %Box Elder County0.3Iron County: 0.3 %Iron County0.3San Juan County: 0.3 %San Juan County0.3Tooele County: 0.3 %Tooele County0.3Utah County: 0.3 %Utah County0.3Wasatch County: 0.3 %Wasatch County0.3Cache County: 0 %Cache County0Garfield County: 0 %Garfield County0Grand County: 0 %Grand County0Washington County: 0 %Washington County0Wayne County: 0 %Wayne County0
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2025 (%)Change on 2024
1Salt Lake County4.4-7.3 pts
2Davis County1.9-2.2 pts
3Uintah County1.1-0.8 pts
4Carbon County0.5+0.2 pts
4Duchesne County0.5-0.9 pts
4Weber County0.5-1.1 pts
7Box Elder County0.3-1.1 pts
7Iron County0.3+0.3 pts
7San Juan County0.3-0.5 pts
7Tooele County0.3-3 pts
7Utah County0.3-2.2 pts
7Wasatch County0.3-0.4 pts
13Cache County0-0.3 pts
13Garfield County00 pts
13Grand County0-0.5 pts
13Washington County0-0.5 pts
13Wayne County00 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. 2 counties with data in other periods have no value for 2025 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 Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025) [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 Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025. 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/utah-counties. 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 Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025. 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/utah-counties.

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 Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/unhealthy-air-quality-days-share/utah-counties (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_utah_by_2025,
  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 Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025}},
  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/utah-counties. 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 Utah by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025
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/utah-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/utah-counties.
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 Utah 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":"Utah","limit":10}
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Questions

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

Salt Lake County, with 4.4% in 2025, according to EPA.

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

Wayne County, with 0% in 2025.

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. 2 counties have no value for 2025 and are not ranked.

Share of days unhealthy for sensitive groups or worse (US EPA AQI): other rankings

Counties in Utah: more rankings