Median AQI
12
Good
Montana · County air quality · 2025
Beaverhead County, Montana
Median AQI 12 (Good). 100.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 12
- Median AQI
- 100.0%
- Good-air days
- 0
- Unhealthy days
- 96%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Beaverhead County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 12 with 100.0% of 175 monitored days in the Good band, driven mainly by PM2.5.
- 12
- median AQI · Good
- 100.0%
- days rated Good
- PM2.5
- main pollutant
- 96%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 48.
Data updated July 2026
- Good · 175 d · 100.0%
How did Beaverhead County's air break down in 2025?
Across 175 monitored days, 175 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 48 (Good).
EPA AQS →Air quality data from EPA Air Quality System (2025). 175 days monitored. Median AQI: 12 (Good).
Insights: Beaverhead County, Montana. EPA monitors recorded a median Air Quality Index of 12 across 175 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 175 (100%) fell in the Good band (AQI 0–50), 0 (0%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 23, while the worst single-day peak hit 48 (Good). Residents averaged about 30.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (175 days). Across the 2023–2025 trend window, good days shifted by -169 and the median AQI moved -1 points, placing the multi-year trajectory at improving. The worst single reading over the 2023–2025 window was AQI 48, good but never Unhealthy. Nearby counties show comparable readings: Custer (91.2% good, AQI 39); Dawson (95.0% good, AQI 14); Fergus (92.2% good, AQI 44); Flathead (82.1% good, AQI 40); Gallatin (99.1% good, AQI 14); Glacier (96.4% good, AQI 22).
Air Quality Summary
Good Days
100.0%
175 of 175 monitored days
25.0pp vs 75% target
Max AQI Recorded
48
Good
Health Grade
Excellent
90th-pct AQI 23
Beaverhead County, Good days share 100.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Beaverhead 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 175 monitored days across EPA AQI categories.
Good
175
100%
Moderate
0
0%
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 Beaverhead County.
- PM2.5 · 175 days · 100.0%
Health Impact Assessment
Excellent
Beaverhead County's air quality is rated Excellent based on 100.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 100.0% of monitored days in 2025, with a median AQI of 12. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 175 of 175 monitored days.
5-Year Air Quality Trend
Air quality is improving in Beaverhead County. Best year: 2023 (344 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2023 | 344 | 12 | 2 | 0 | 13 | 124 |
| 2024 | 298 | 46 | 0 | 2 | 12 | 180 |
| 2025 | 175 | 0 | 0 | 0 | 12 | 48 |
How does Beaverhead County compare?
How Beaverhead County compares
Good-day share better than US avg
Beaverhead County 100.0%
Custer County, Montana 91.2%
US average 76.5%
Median AQI better than US avg
Beaverhead County 12
Custer County, Montana 39
US average 38
Unhealthy days / yr about average
Beaverhead County 0
Custer County, Montana 0
US average 0
Other Counties in Montana
Air quality comparison for nearby counties in Montana.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Beaverhead County.
Columbiana County, Ohio
AQI 12 · 100.0% good
Cook County, Minnesota
AQI 12 · 100.0% good
Mayagnez County, Puerto Rico
AQI 12 · 96.9% good
Navajo County, Arizona
AQI 12 · 99.6% good
Socorro County, New Mexico
AQI 12 · 100.0% good
Windham County, Vermont
AQI 12 · 100.0% good
What Beaverhead County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 12 means for exposure. Health guidance
- See how Beaverhead County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Beaverhead County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 175 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 Beaverhead County, Montana? ▼
Beaverhead County has a median Air Quality Index (AQI) of 12, rated "Good." 100.0% of monitored days (175 out of 175) had good air quality in 2025.
What is the main pollutant in Beaverhead County? ▼
The primary pollutant in Beaverhead County is Fine Particles (PM2.5), which was the main AQI driver on 175 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Beaverhead County have? ▼
In 2025, Beaverhead County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 48.
Is the air quality in Beaverhead County getting better or worse? ▼
Air quality in Beaverhead County is improving based on 5-year trends (2023-2025). Best year: 2023 with 344 good days. Worst year: 2025 with 175 good days.
What does AQI 12 mean for health? ▼
Beaverhead County's median AQI of 12 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 Beaverhead County compare to other counties in Montana? ▼
Beaverhead County has 100.0% good air days. Nearby counties in Montana: Custer (91.2% good), Dawson (95.0% good), Fergus (92.2% good), Flathead (82.1% good), Gallatin (99.1% good), Glacier (96.4% good).
What is the 90th percentile AQI in Beaverhead County? ▼
The 90th percentile AQI for Beaverhead County is 23, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 48 (Good).
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.