Bad Air Days in Silver Bow County, Montana: 7 a Year
7 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 135 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (100% particle days).
When the bad days come in Silver Bow
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in September and August and July. Averaged over 2016 to 2025.
What actually helps here
- Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
- Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.
The record for Silver Bow
In 2000 to 2009 this county averaged 4 bad days a year; in 2016 to 2025, 7. It has got worse. The worst recent year was 2017, with 24 bad days on 354 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2017-09-03 | 191 | PM2.5 |
| 2020-09-16 | 181 | PM2.5 |
| 2017-09-02 | 174 | PM2.5 |
| 2024-09-10 | 168 | PM2.5 |
| 2020-09-15 | 167 | PM2.5 |
Most days, not the worst ones
Across 3,638 monitored days from 2016 to 2025, the air in Silver Bow County rated Good on 74% of them, close to the 72% typical of monitored counties, and Moderate on 24%. The median day sat at AQI 30; one day in ten went above 67.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)84%3,046 days
- coarse dust (PM10)16%592 days
Silver Bow County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 310 | 55 | 0 | 0 | 28 | 96 |
| 2024 | 366 | 258 | 103 | 5 | 2 | 31 | 168 |
| 2023 | 365 | 268 | 94 | 3 | 0 | 31 | 124 |
| 2022 | 365 | 268 | 87 | 10 | 2 | 27 | 162 |
| 2021 | 365 | 256 | 89 | 20 | 6 | 33 | 163 |
| 2020 | 366 | 289 | 69 | 8 | 3 | 22 | 181 |
| 2019 | 363 | 293 | 70 | 0 | 0 | 24 | 92 |
| 2018 | 363 | 284 | 78 | 1 | 0 | 25 | 120 |
| 2017 | 354 | 188 | 142 | 24 | 4 | 46 | 191 |
| 2016 | 366 | 283 | 83 | 0 | 0 | 29 | 94 |
| 2015 | 365 | 239 | 116 | 10 | 6 | 39 | 175 |
| 2014 | 362 | 232 | 129 | 1 | 0 | 40 | 108 |
| 2013 | 365 | 238 | 121 | 6 | 1 | 37 | 153 |
| 2012 | 363 | 225 | 125 | 13 | 5 | 39 | 183 |
| 2011 | 364 | 233 | 126 | 5 | 0 | 41 | 135 |
| 2010 | 362 | 224 | 124 | 14 | 0 | 39 | 139 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Missoula County18/yr
- Ravalli County11/yr
- Lewis and Clark County9/yr
- Lincoln County8/yr
- Sanders County7/yr
- Powder River County6/yr
- Flathead County6/yr
- Lake Countythin data
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day.