Median AQI
14
Good
Montana · County air quality · 2025
Gallatin County, Montana
Median AQI 14 (Good). 99.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 14
- Median AQI
- 99.1%
- Good-air days
- 0
- Unhealthy days
- 95%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Gallatin County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 14 with 99.1% of 226 monitored days in the Good band, driven mainly by PM2.5.
- 14
- median AQI · Good
- 99.1%
- days rated Good
- PM2.5
- main pollutant
- 95%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 62.
Data updated July 2026
- Good · 224 d · 99.1%
- Moderate · 2 d · 0.9%
How did Gallatin County's air break down in 2025?
Across 226 monitored days, 224 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 62 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 226 days monitored. Median AQI: 14 (Good).
Insights: Gallatin County, Montana. EPA monitors recorded a median Air Quality Index of 14 across 226 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 224 (99%) fell in the Good band (AQI 0–50), 2 (1%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 25, while the worst single-day peak hit 62 (Moderate). Residents averaged about 29.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (180 days), NO2 (43 days), CO (3 days). Across the 2020–2025 trend window, good days shifted by -66 and the median AQI moved -15 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 62, moderate but never Unhealthy. Nearby counties show comparable readings: Beaverhead (100.0% good, AQI 12); Custer (91.2% good, AQI 39); Dawson (95.0% good, AQI 14); Fergus (92.2% good, AQI 44); Flathead (82.1% good, AQI 40); Glacier (96.4% good, AQI 22).
Air Quality Summary
Good Days
99.1%
224 of 226 monitored days
24.1pp vs 75% target
Max AQI Recorded
62
Moderate
Health Grade
Excellent
90th-pct AQI 25
Gallatin County, Good days share 99.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Gallatin 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 226 monitored days across EPA AQI categories.
Good
224
99%
Moderate
2
1%
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 Gallatin County.
- PM2.5 · 180 days · 79.6%
- NO₂ · 43 days · 19.0%
- CO · 3 days · 1.3%
Health Impact Assessment
Excellent
Gallatin County's air quality is rated Excellent based on 99.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 99.1% of monitored days in 2025, with a median AQI of 14. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 180 of 226 monitored days.
5-Year Air Quality Trend
Air quality is improving in Gallatin County. Best year: 2023 (331 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 290 | 65 | 9 | 2 | 29 | 162 |
| 2021 | 243 | 107 | 14 | 1 | 41 | 158 |
| 2022 | 290 | 71 | 4 | 0 | 32 | 148 |
| 2023 | 331 | 34 | 0 | 0 | 26 | 98 |
| 2024 | 329 | 36 | 0 | 0 | 18 | 84 |
| 2025 | 224 | 2 | 0 | 0 | 14 | 62 |
How does Gallatin County compare?
How Gallatin County compares
Good-day share better than US avg
Gallatin County 99.1%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI better than US avg
Gallatin County 14
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr about average
Gallatin County 0
Beaverhead 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 Gallatin County.
Apache County, Arizona
AQI 14 · 99.6% good
Dawson County, Montana
AQI 14 · 95.0% good
Hughes County, South Dakota
AQI 14 · 94.4% good
Klickitat County, Washington
AQI 14 · 84.2% good
Park County, Wyoming
AQI 14 · 99.5% good
Platte County, Wyoming
AQI 14 · 87.7% good
What Gallatin 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 14 means for exposure. Health guidance
- See how Gallatin County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Gallatin County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 226 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 Gallatin County, Montana? ▼
Gallatin County has a median Air Quality Index (AQI) of 14, rated "Good." 99.1% of monitored days (224 out of 226) had good air quality in 2025.
What is the main pollutant in Gallatin County? ▼
The primary pollutant in Gallatin County is Fine Particles (PM2.5), which was the main AQI driver on 180 days (80% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Gallatin County have? ▼
In 2025, Gallatin County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 62.
Is the air quality in Gallatin County getting better or worse? ▼
Air quality in Gallatin County is improving based on 5-year trends (2020-2025). Best year: 2023 with 331 good days. Worst year: 2025 with 224 good days.
What does AQI 14 mean for health? ▼
Gallatin County's median AQI of 14 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 Gallatin County compare to other counties in Montana? ▼
Gallatin County has 99.1% good air days. Nearby counties in Montana: Beaverhead (100.0% good), Custer (91.2% good), Dawson (95.0% good), Fergus (92.2% good), Flathead (82.1% good), Glacier (96.4% good).
What is the 90th percentile AQI in Gallatin County? ▼
The 90th percentile AQI for Gallatin County is 25, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 62 (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.