Median AQI
27
Good
Montana · County air quality · 2025
Silver Bow County, Montana
Median AQI 27 (Good). 82.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 27
- Median AQI
- 82.9%
- Good-air days
- 0
- Unhealthy days
- 60%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Silver Bow County's air is good on balance, cleaner than the median US county, a median AQI of 27 with 82.9% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 27
- median AQI · Good
- 82.9%
- days rated Good
- PM2.5
- main pollutant
- 60%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 77.
Data updated July 2026
- Good · 150 d · 82.9%
- Moderate · 31 d · 17.1%
How did Silver Bow County's air break down in 2025?
Across 181 monitored days, 150 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 77 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 27 (Good).
Insights: Silver Bow County, Montana. EPA monitors recorded a median Air Quality Index of 27 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 150 (83%) fell in the Good band (AQI 0–50), 31 (17%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 54, while the worst single-day peak hit 77 (Moderate). Residents averaged about 24.9 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (173 days), PM10 (8 days). Across the 2020–2025 trend window, good days shifted by -139 and the median AQI moved +5 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 77, 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
82.9%
150 of 181 monitored days
7.9pp vs 75% target
Max AQI Recorded
77
Moderate
Health Grade
Good
90th-pct AQI 54
Silver Bow County, Good days share 82.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Silver Bow 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
150
83%
Moderate
31
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 Silver Bow County.
- PM2.5 · 173 days · 95.6%
- PM10 · 8 days · 4.4%
Health Impact Assessment
Good
Silver Bow County's air quality is rated Good based on 82.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 82.9% of monitored days in 2025, with a median AQI of 27. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 173 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Silver Bow County. Best year: 2020 (289 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 289 | 69 | 5 | 3 | 22 | 181 |
| 2021 | 256 | 89 | 14 | 6 | 33 | 163 |
| 2022 | 268 | 87 | 8 | 2 | 27 | 162 |
| 2023 | 268 | 94 | 3 | 0 | 31 | 124 |
| 2024 | 258 | 103 | 3 | 2 | 31 | 168 |
| 2025 | 150 | 31 | 0 | 0 | 27 | 77 |
How does Silver Bow County compare?
How Silver Bow County compares
Good-day share better than US avg
Silver Bow County 82.9%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI better than US avg
Silver Bow County 27
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr about average
Silver Bow 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 Silver Bow County.
Chelan County, Washington
AQI 27 · 87.2% good
Clackamas County, Oregon
AQI 27 · 93.9% good
Stevens County, Washington
AQI 27 · 81.1% good
Clallam County, Washington
AQI 26 · 88.5% good
Delta County, Colorado
AQI 28 · 88.0% good
Ford County, Kansas
AQI 26 · 89.4% good
What Silver Bow 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 27 means for exposure. Health guidance
- See how Silver Bow County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Silver Bow 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 Silver Bow County, Montana? ▼
Silver Bow County has a median Air Quality Index (AQI) of 27, rated "Good." 82.9% of monitored days (150 out of 181) had good air quality in 2025.
What is the main pollutant in Silver Bow County? ▼
The primary pollutant in Silver Bow County is Fine Particles (PM2.5), which was the main AQI driver on 173 days (96% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Silver Bow County have? ▼
In 2025, Silver Bow County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 77.
Is the air quality in Silver Bow County getting better or worse? ▼
Air quality in Silver Bow County is improving based on 5-year trends (2020-2025). Best year: 2020 with 289 good days. Worst year: 2025 with 150 good days.
What does AQI 27 mean for health? ▼
Silver Bow County's median AQI of 27 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 Silver Bow County compare to other counties in Montana? ▼
Silver Bow County has 82.9% 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 Silver Bow County? ▼
The 90th percentile AQI for Silver Bow County is 54, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 77 (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.