Median AQI
38
Good
Montana · County air quality · 2025
Missoula County, Montana
Median AQI 38 (Good). 83.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 83.4%
- Good-air days
- 0
- Unhealthy days
- 61%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Missoula County's air is good on balance, cleaner than the median US county, a median AQI of 38 with 83.4% of 181 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 83.4%
- days rated Good
- Ozone
- main pollutant
- 61%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 82.
Data updated July 2026
- Good · 151 d · 83.4%
- Moderate · 30 d · 16.6%
How did Missoula County's air break down in 2025?
Across 181 monitored days, 151 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 82 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 38 (Good).
Insights: Missoula County, Montana. EPA monitors recorded a median Air Quality Index of 38 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 151 (83%) fell in the Good band (AQI 0–50), 30 (17%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 56, while the worst single-day peak hit 82 (Moderate). Residents averaged about 25.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (103 days), PM2.5 (78 days). Across the 2020–2025 trend window, good days shifted by -4 and the median AQI moved -16 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 82, 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); Gallatin (99.1% good, AQI 14).
Air Quality Summary
Good Days
83.4%
151 of 181 monitored days
8.4pp vs 75% target
Max AQI Recorded
82
Moderate
Health Grade
Good
90th-pct AQI 56
Missoula County, Good days share 83.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Missoula 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 181 monitored days across EPA AQI categories.
Good
151
83%
Moderate
30
17%
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 Missoula County.
- Ozone · 103 days · 56.9%
- PM2.5 · 78 days · 43.1%
Health Impact Assessment
Good
Missoula County's air quality is rated Good based on 83.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 83.4% of monitored days in 2025, with a median AQI of 38. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 103 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Missoula County. Best year: 2024 (237 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 155 | 192 | 13 | 6 | 54 | 185 |
| 2021 | 122 | 213 | 24 | 6 | 56 | 162 |
| 2022 | 149 | 201 | 11 | 4 | 54 | 190 |
| 2023 | 156 | 200 | 8 | 0 | 53 | 134 |
| 2024 | 237 | 125 | 3 | 1 | 43 | 153 |
| 2025 | 151 | 30 | 0 | 0 | 38 | 82 |
How does Missoula County compare?
How Missoula County compares
Good-day share better than US avg
Missoula County 83.4%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI about average
Missoula County 38
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr about average
Missoula 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 Missoula County.
Adams County, Illinois
AQI 38 · 94.4% good
Anoka County, Minnesota
AQI 38 · 82.1% good
Atlantic County, New Jersey
AQI 38 · 79.6% good
Avery County, North Carolina
AQI 38 · 93.9% good
Barnstable County, Massachusetts
AQI 38 · 92.5% good
Bay County, Michigan
AQI 38 · 71.8% good
What Missoula 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 38 means for exposure. Health guidance
- See how Missoula County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Missoula County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 181 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 Missoula County, Montana? ▼
Missoula County has a median Air Quality Index (AQI) of 38, rated "Good." 83.4% of monitored days (151 out of 181) had good air quality in 2025.
What is the main pollutant in Missoula County? ▼
The primary pollutant in Missoula County is Ozone (O3), which was the main AQI driver on 103 days (57% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Missoula County have? ▼
In 2025, Missoula County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 82.
Is the air quality in Missoula County getting better or worse? ▼
Air quality in Missoula County is improving based on 5-year trends (2020-2025). Best year: 2024 with 237 good days. Worst year: 2021 with 122 good days.
What does AQI 38 mean for health? ▼
Missoula County's median AQI of 38 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 Missoula County compare to other counties in Montana? ▼
Missoula County has 83.4% 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), Gallatin (99.1% good).
What is the 90th percentile AQI in Missoula County? ▼
The 90th percentile AQI for Missoula County is 56, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 82 (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.