Median AQI
48
Good
Utah · County air quality · 2025
Box Elder County, Utah
Median AQI 48 (Good). 60.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 48
- Median AQI
- 60.0%
- Good-air days
- 0
- Unhealthy days
- 15%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Box Elder County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 48 with 60.0% of 305 monitored days in the Good band, driven mainly by Ozone.
- 48
- median AQI · Good
- 60.0%
- days rated Good
- Ozone
- main pollutant
- 15%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 105.
Data updated July 2026
- Good · 183 d · 60.0%
- Moderate · 121 d · 39.7%
- USG · 1 d · 0.3%
How did Box Elder County's air break down in 2025?
Across 305 monitored days, 183 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 105 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 305 days monitored. Median AQI: 48 (Good).
Insights: Box Elder County, Utah. EPA monitors recorded a median Air Quality Index of 48 across 305 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 183 (60%) fell in the Good band (AQI 0–50), 121 (40%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 71, while the worst single-day peak hit 105 (USG). Residents averaged about 18.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (271 days), PM2.5 (29 days), PM10 (4 days), NO2 (1 days). Across the 2020–2025 trend window, good days shifted by -133 and the median AQI moved +8 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 105, usg but never Unhealthy. Nearby counties show comparable readings: 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); Grand (61.7% good, AQI 47).
Air Quality Summary
Good Days
60.0%
183 of 305 monitored days
-15.0pp vs 75% target
Max AQI Recorded
105
USG
Health Grade
Moderate
90th-pct AQI 71
Box Elder County, Good days share 60.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Box Elder 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 305 monitored days across EPA AQI categories.
Good
183
60%
Moderate
121
40%
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 Box Elder County.
- Ozone · 271 days · 88.9%
- PM2.5 · 29 days · 9.5%
- PM10 · 4 days · 1.3%
- NO₂ · 1 days · 0.3%
Health Impact Assessment
Moderate
Box Elder County's air quality is rated Moderate based on 60.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 60.0% of monitored days in 2025, with a median AQI of 48. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 271 of 305 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Box Elder County. Best year: 2020 (316 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 316 | 36 | 3 | 0 | 40 | 147 |
| 2021 | 281 | 78 | 4 | 0 | 42 | 119 |
| 2022 | 266 | 15 | 0 | 0 | 35 | 90 |
| 2023 | 302 | 58 | 0 | 0 | 38 | 96 |
| 2024 | 214 | 147 | 5 | 0 | 47 | 133 |
| 2025 | 183 | 121 | 1 | 0 | 48 | 105 |
How does Box Elder County compare?
How Box Elder County compares
Good-day share worse than US avg
Box Elder County 60.0%
Cache County, Utah 61.2%
US average 76.5%
Median AQI worse than US avg
Box Elder County 48
Cache County, Utah 46
US average 38
Unhealthy days / yr about average
Box Elder County 0
Cache 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 Box Elder County.
Black Hawk County, Iowa
AQI 48 · 56.6% good
Brookings County, South Dakota
AQI 48 · 53.0% good
Clear Creek County, Colorado
AQI 48 · 64.4% good
Coconino County, Arizona
AQI 48 · 62.5% good
Columbia County, Florida
AQI 48 · 56.4% good
Davis County, Utah
AQI 48 · 59.5% good
What Box Elder 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 48 means for exposure. Health guidance
- See how Box Elder County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Box Elder County with its Utah neighbours before drawing a conclusion about the region. All of Utah
Based on 305 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 Box Elder County, Utah? ▼
Box Elder County has a median Air Quality Index (AQI) of 48, rated "Good." 60.0% of monitored days (183 out of 305) had good air quality in 2025.
What is the main pollutant in Box Elder County? ▼
The primary pollutant in Box Elder County is Ozone (O3), which was the main AQI driver on 271 days (89% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Box Elder County have? ▼
In 2025, Box Elder County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 105.
Is the air quality in Box Elder County getting better or worse? ▼
Air quality in Box Elder County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 316 good days. Worst year: 2025 with 183 good days.
What does AQI 48 mean for health? ▼
Box Elder County's median AQI of 48 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 Box Elder County compare to other counties in Utah? ▼
Box Elder County has 60.0% good air days. Nearby counties in Utah: Cache (61.2% good), Carbon (62.9% good), Davis (59.5% good), Duchesne (59.4% good), Garfield (100.0% good), Grand (61.7% good).
What is the 90th percentile AQI in Box Elder County? ▼
The 90th percentile AQI for Box Elder County is 71, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 105 (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.