Median AQI
47
Good
Utah · County air quality · 2025
Grand County, Utah
Median AQI 47 (Good). 61.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 47
- Median AQI
- 61.7%
- Good-air days
- 0
- Unhealthy days
- 18%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Grand County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 47 with 61.7% of 303 monitored days in the Good band, driven mainly by Ozone.
- 47
- median AQI · Good
- 61.7%
- days rated Good
- Ozone
- main pollutant
- 18%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 93.
Data updated July 2026
- Good · 187 d · 61.7%
- Moderate · 116 d · 38.3%
How did Grand County's air break down in 2025?
Across 303 monitored days, 187 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 93 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 303 days monitored. Median AQI: 47 (Good).
Insights: Grand County, Utah. EPA monitors recorded a median Air Quality Index of 47 across 303 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 187 (62%) fell in the Good band (AQI 0–50), 116 (38%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 64, while the worst single-day peak hit 93 (Moderate). Residents averaged about 18.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (205 days), PM2.5 (98 days). Across the 2023–2025 trend window, good days shifted by +43 and the median AQI moved -2 points, placing the multi-year trajectory at improving. The worst single reading over the 2023–2025 window was AQI 93, moderate 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
61.7%
187 of 303 monitored days
-13.3pp vs 75% target
Max AQI Recorded
93
Moderate
Health Grade
Moderate
90th-pct AQI 64
Grand County, Good days share 61.7%
National avg
Share of monitored days at AQI 0-50 (Good band).
Grand 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 303 monitored days across EPA AQI categories.
Good
187
62%
Moderate
116
38%
USG
0
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 Grand County.
- Ozone · 205 days · 67.7%
- PM2.5 · 98 days · 32.3%
Health Impact Assessment
Moderate
Grand County's air quality is rated Moderate based on 61.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 61.7% of monitored days in 2025, with a median AQI of 47. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 205 of 303 monitored days.
5-Year Air Quality Trend
Air quality is improving in Grand County. Best year: 2024 (246 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2023 | 144 | 117 | 0 | 0 | 49 | 80 |
| 2024 | 246 | 117 | 2 | 0 | 47 | 105 |
| 2025 | 187 | 116 | 0 | 0 | 47 | 93 |
How does Grand County compare?
How Grand County compares
Good-day share worse than US avg
Grand County 61.7%
Box Elder County, Utah 60.0%
US average 76.5%
Median AQI worse than US avg
Grand County 47
Box Elder County, Utah 48
US average 38
Unhealthy days / yr about average
Grand 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 Grand County.
Beaver County, Pennsylvania
AQI 47 · 54.3% good
Bell County, Texas
AQI 47 · 61.3% good
Bowie County, Texas
AQI 47 · 57.3% good
Bronx County, New York
AQI 47 · 56.6% good
Butte County, California
AQI 47 · 66.1% good
Calcasieu County, Louisiana
AQI 47 · 61.5% good
What Grand 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 47 means for exposure. Health guidance
- See how Grand County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Grand County with its Utah neighbours before drawing a conclusion about the region. All of Utah
Based on 303 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 Grand County, Utah? ▼
Grand County has a median Air Quality Index (AQI) of 47, rated "Good." 61.7% of monitored days (187 out of 303) had good air quality in 2025.
What is the main pollutant in Grand County? ▼
The primary pollutant in Grand County is Ozone (O3), which was the main AQI driver on 205 days (68% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Grand County have? ▼
In 2025, Grand County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 93.
Is the air quality in Grand County getting better or worse? ▼
Air quality in Grand County is improving based on 5-year trends (2023-2025). Best year: 2024 with 246 good days. Worst year: 2023 with 144 good days.
What does AQI 47 mean for health? ▼
Grand County's median AQI of 47 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 Grand County compare to other counties in Utah? ▼
Grand County has 61.7% 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 Grand County? ▼
The 90th percentile AQI for Grand County is 64, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 93 (Moderate).
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.