State air quality · 2025
Utah Air Quality Ranking
Across 17 monitored counties, the typical county in Utah posts a median AQI of 42 (Good) and 65.4% of monitored days were rated Good, from EPA AQS.
- 42
- Avg median AQI
- 65.4%
- Good-air days
- 17
- Counties monitored
- 4%
- Cleaner than US states
Utah's typical county median AQI is 42 (Good) across 17 monitored counties
According to the U.S. EPA Air Quality System, Utah monitors 17 counties with a day-weighted Good-day share of 65.4%. Cleanest: San Juan County (75.9% Good). Most polluted: Salt Lake County (33.1%). These are annual summaries, not live AirNow readings.
Data source EPA Air Quality System (AQS)
- Cleaner than US states
- Utah's day-weighted Good-day share of 65.4% places it cleaner than 4% of US states.
- In-state spread
- Within Utah, Wayne County leads at 97.9% Good days while Salt Lake County sits at 33.1% across 17 monitored counties.
- 2024→2025 release
- Utah's Good-day share moved -2.0 points vs the 2024 EPA annual release.
- Typical median AQI
- Typical median AQI: 42
Verify with AirNow → · EPA AQS →
EPA state monitoring brief
AQS state key UTAH
Utah · 2025 EPA AQS · 17 counties · med AQI 42 · 65.4% Good · San Juan→Salt Lake spread
- GOOD 42 Median AQI · Good
- SHARE 65.4% Good-day share
- COUNT 17 Counties monitored
- UNH 1 Unhealthy+ days
- RANK 4% Cleaner than states
- O3 78.0% Main pollutant share
Good-day share peers
Utah's 65.4% Good-day share is cleaner than 4% of monitored US states; San Juan and Salt Lake County bracket the in-state range. Open Wayne County →
According to EPA AQS annual summaries on PlainAirData, Utah ranks #49 of 52 by day-weighted good-day share (65.4%) and #43 by mean county median AQI (42.2). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).
Data updated August 2026
What changed, what drives it, and how thick is the sample
Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.
Release change
65.4%
Good-day share in 2025, down 2.0 percentage points vs 2024. County-mean median AQI 42, 0.8 points higher (worse) than 2024.
Pollutant mix
Ozone
Main driver on 78.0% of pollutant-assigned days.
- Ozone 78.0%
- PM2.5 20.1%
- NO2 1.2%
- PM10 0.7%
Monitoring coverage
332
Average monitored days per county in the latest release. 2 of 17 counties sit below the 100-day floor used for cleanest/most-polluted claims.
Counties Monitored
17
Good Days %
65.4%
Avg Median AQI
42
Total Unhealthy Days
1
Best Air Quality
San Juan County
Worst Air Quality
Salt Lake County
Where Utah sits nationally
COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Utah's day-weighted Good-day share is 65.4% - cleaner than 4% of that comparison set.
Utah Good-day share vs. every US state
Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
65.4% 4th percentile higher than 4% of 52 US states
Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Which counties in Utah have the cleanest and most polluted air?
Cleanest counties in Utah
| County | Good % | Median AQI | Max AQI | Unhealthy Days |
|---|---|---|---|---|
| Wayne | 97.9% | 14 | 57 | 0 |
| Garfield | 97.7% | 12 | 79 | 0 |
| San Juan | 75.9% | 44 | 108 | 0 |
| Washington | 75.1% | 44 | 97 | 0 |
| Iron | 74.7% | 44 | 105 | 0 |
| Tooele | 74.3% | 44 | 101 | 0 |
| Carbon | 72.3% | 44 | 108 | 0 |
| Cache | 66.0% | 44 | 87 | 0 |
| Wasatch | 65.8% | 45 | 105 | 0 |
| Weber | 65.8% | 45 | 119 | 0 |
| Box Elder | 64.7% | 45 | 105 | 0 |
| Davis | 63.3% | 46 | 119 | 0 |
| Grand | 60.2% | 47 | 96 | 0 |
| Duchesne | 59.7% | 46 | 112 | 0 |
| Uintah | 58.4% | 48 | 126 | 0 |
| Utah | 56.4% | 48 | 109 | 0 |
| Salt Lake | 33.1% | 57 | 175 | 1 |
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.
Coverage: 17 counties in Utah with active monitoring stations. Unmonitored counties are not represented.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025
Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.