Median AQI
38
Good
Montana · County air quality · 2025
Missoula County, Montana
Median AQI 38 (Good). 81.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 81.6%
- Good-air days
- 0
- Unhealthy days
- 61%
- Cleaner than US counties
Missoula County's 2025 annual median AQI is 38 (Good), with 81.6% Good days
According to the U.S. EPA Air Quality System, Missoula County, Montana posted a 2025 median AQI of 38 (Good) across 365 monitored days, with 81.6% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Missoula County's 81.6% Good-day share places it cleaner than 61% of US counties in 2025.
- Closest median-AQI peer
- Adams County (94.7% Good, median AQI 38) is the closest nationwide median-AQI peer to Missoula County.
- 2020–2025 trend
- Missoula County's floor-qualifying Good-day share is improving from 2020 to 2025 (42.3% → 81.6%).
- Median AQI
- Median AQI: 38
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 81.6% of 365 monitored days in the Good band, driven mainly by PM2.5.
- 38
- median AQI · Good
- 81.6%
- days rated Good
- PM2.5
- main pollutant
- 61%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 98.
Annual release change
What changed in the 2025 EPA annual release
- Missoula County's Good-day share rose from 64.8% to 81.6% between the 2024 and 2025 EPA annual releases, a change of +16.9 percentage points.
- Missoula County's peak single-day AQI fell from 153 to 98 between the 2024 and 2025 EPA annual releases, a change of -55 points.
- Missoula County's median AQI fell from 43 to 38 between the 2024 and 2025 EPA annual releases, a change of -5 points.
- Missoula County's Unhealthy-category days fell from 1 to 0 between the 2024 and 2025 EPA annual releases, a change of -1 days.
Data updated August 2026
- Good · 298 d · 81.6%
- Moderate · 67 d · 18.4%
How did Missoula County's air break down in 2025?
Across 365 monitored days, 298 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 98 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 38 (Good).
Insights: Missoula County, Montana. EPA monitors recorded a median Air Quality Index of 38 across 365 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 298 (82%) fell in the Good band (AQI 0–50), 67 (18%) 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 98 (Moderate). Residents averaged about 24.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (188 days), Ozone (177 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +39.3 points 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 98, moderate but never Unhealthy. Nearby counties show comparable readings: Beaverhead (94.7% good, AQI 13); Cascade (59.8% good, AQI 46); Custer (87.2% good, AQI 40); Dawson (90.3% good, AQI 18); Fergus (90.7% good, AQI 41); Flathead (73.7% good, AQI 41).
Air Quality Summary
Good Days
81.6%
298 of 365 monitored days
6.6pp vs 75% target
Max AQI Recorded
98
Moderate
Health Grade
Good
90th-pct AQI 56
Missoula County, Good days share 81.6%
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 365 monitored days across EPA AQI categories.
Good
298
82%
Moderate
67
18%
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.
- PM2.5 · 188 days · 51.5%
- Ozone · 177 days · 48.5%
Health Impact Assessment
Good
Missoula County's air quality is rated Good based on 81.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 81.6% 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 PM2.5, driving AQI on 188 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Missoula County. Highest Good-day share: 2025 (81.6%, 298 of 365 monitored 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 | 298 | 67 | 0 | 0 | 38 | 98 |
How does Missoula County compare?
How Missoula County compares
Good-day share better than typical
Missoula County 81.6%
Adams County, Illinois 94.7%
Typical US county 76.0%
Median AQI better than typical
Missoula County 38
Adams County, Illinois 38
Typical US county 39
Unhealthy days / yr better than typical
Missoula County 0
Adams County, Illinois 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Missoula County (38), not geographic neighbors.
Adams County, Illinois
Median AQI 38 · 94.7% Good-day share
Albemarle County, Virginia
Median AQI 38 · 81.0% Good-day share
Alexander County, North Carolina
Median AQI 38 · 93.5% Good-day share
Amador County, California
Median AQI 38 · 87.4% Good-day share
Anoka County, Minnesota
Median AQI 38 · 74.1% Good-day share
Avery County, North Carolina
Median AQI 38 · 92.3% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Cedar County, Missouri
81.6% Good-day share · median AQI 39
Carter County, Oklahoma
81.6% Good-day share · median AQI 32
Guaynabo County, Puerto Rico
81.6% Good-day share · median AQI 33
Mitchell County, North Carolina
81.5% Good-day share · median AQI 31
Del Norte County, California
81.8% Good-day share · median AQI 32
Lawrence County, Tennessee
81.5% Good-day share · median AQI 33
Montana counties on the map
Geographic containment only, other monitored counties in Montana, independent of AQI or pollutant match.
What Missoula 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 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 365 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
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." 81.6% of monitored days (298 out of 365) had good air quality in 2025.
What is the main pollutant in Missoula County? ▼
The primary pollutant in Missoula County is Fine Particles (PM2.5), which was the main AQI driver on 188 days (52% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
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 98.
Is the air quality in Missoula County getting better or worse? ▼
Air quality in Missoula County is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 81.6% (298 of 365 days). Lowest qualifying Good-day share: 2021 at 33.4% (122 of 365 days).
What does AQI 38 mean for health? ▼
Missoula County's median AQI of 38 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Missoula County compare to other counties in Montana? ▼
Missoula County has 81.6% good air days. Nearby counties in Montana: Beaverhead (94.7% good), Cascade (59.8% good), Custer (87.2% good), Dawson (90.3% good), Fergus (90.7% good), Flathead (73.7% 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 98 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Missoula County, Montana · 2020–2025
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Every figure on PlainAirData 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.