Median AQI
46
Good
Utah · County air quality · 2025
San Juan County, Utah
Median AQI 46 (Good). 65.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 46
- Median AQI
- 65.3%
- Good-air days
- 0
- Unhealthy days
- 23%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, San Juan County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 46 with 65.3% of 219 monitored days in the Good band, driven mainly by Ozone.
- 46
- median AQI · Good
- 65.3%
- days rated Good
- Ozone
- main pollutant
- 23%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 108.
Data updated July 2026
- Good · 143 d · 65.3%
- Moderate · 75 d · 34.2%
- USG · 1 d · 0.5%
How did San Juan County's air break down in 2025?
Across 219 monitored days, 143 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 219 days monitored. Median AQI: 46 (Good).
Insights: San Juan County, Utah. EPA monitors recorded a median Air Quality Index of 46 across 219 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 143 (65%) fell in the Good band (AQI 0–50), 75 (34%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 67, while the worst single-day peak hit 108 (USG). Residents averaged about 19.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (219 days). Across the 2020–2025 trend window, good days shifted by -151 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 108, usg but never Unhealthy. Nearby counties show comparable readings: Box Elder (60.0% good, AQI 48); Cache (61.2% good, AQI 46); Carbon (62.9% good, AQI 47); Davis (59.5% good, AQI 48); Duchesne (59.4% good, AQI 47); Garfield (100.0% good, AQI 4).
Air Quality Summary
Good Days
65.3%
143 of 219 monitored days
-9.7pp vs 75% target
Max AQI Recorded
108
USG
Health Grade
Moderate
90th-pct AQI 67
San Juan County, Good days share 65.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
San Juan County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 219 monitored days across EPA AQI categories.
Good
143
65%
Moderate
75
34%
USG
1
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in San Juan County.
- Ozone · 219 days · 100.0%
Health Impact Assessment
Moderate
San Juan County's air quality is rated Moderate based on 65.3% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 65.3% of monitored days in 2025, with a median AQI of 46. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 219 of 219 monitored days.
5-Year Air Quality Trend
Air quality is worsening in San Juan County. Best year: 2022 (306 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 294 | 67 | 2 | 0 | 43 | 119 |
| 2021 | 276 | 86 | 2 | 0 | 44 | 115 |
| 2022 | 306 | 59 | 0 | 0 | 44 | 87 |
| 2023 | 267 | 90 | 0 | 0 | 45 | 87 |
| 2024 | 276 | 77 | 3 | 0 | 44 | 126 |
| 2025 | 143 | 75 | 1 | 0 | 46 | 108 |
How does San Juan County compare?
How San Juan County compares
Good-day share worse than US avg
San Juan County 65.3%
Box Elder County, Utah 60.0%
US average 76.5%
Median AQI worse than US avg
San Juan County 46
Box Elder County, Utah 48
US average 38
Unhealthy days / yr about average
San Juan County 0
Box Elder County, Utah 0
US average 0
Other Counties in Utah
Air quality comparison for nearby counties in Utah.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to San Juan County.
Bay County, Florida
AQI 46 · 60.6% good
Blount County, Tennessee
AQI 46 · 69.6% good
Cache County, Utah
AQI 46 · 61.2% good
Chesterfield County, South Carolina
AQI 46 · 61.2% good
Clark County, Indiana
AQI 46 · 59.7% good
Clark County, Ohio
AQI 46 · 59.4% good
What San Juan County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 46 means for exposure. Health guidance
- See how San Juan County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare San Juan County with its Utah neighbours before drawing a conclusion about the region. All of Utah
Based on 219 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in San Juan County, Utah? ▼
San Juan County has a median Air Quality Index (AQI) of 46, rated "Good." 65.3% of monitored days (143 out of 219) had good air quality in 2025.
What is the main pollutant in San Juan County? ▼
The primary pollutant in San Juan County is Ozone (O3), which was the main AQI driver on 219 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does San Juan County have? ▼
In 2025, San Juan County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 108.
Is the air quality in San Juan County getting better or worse? ▼
Air quality in San Juan County is worsening based on 5-year trends (2020-2025). Best year: 2022 with 306 good days. Worst year: 2025 with 143 good days.
What does AQI 46 mean for health? ▼
San Juan County's median AQI of 46 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does San Juan County compare to other counties in Utah? ▼
San Juan County has 65.3% good air days. Nearby counties in Utah: Box Elder (60.0% good), Cache (61.2% good), Carbon (62.9% good), Davis (59.5% good), Duchesne (59.4% good), Garfield (100.0% good).
What is the 90th percentile AQI in San Juan County? ▼
The 90th percentile AQI for San Juan County is 67, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 108 (USG).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir 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.