Bad Air Days in Gallatin County, Montana: 5 a Year
5 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 228 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 Gallatin
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in August and September. 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.
The record for Gallatin
In 2000 to 2009 this county averaged 2 bad days a year; in 2016 to 2025, 5. It has got worse. The worst recent year was 2021, with 14 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2016-09-11 | 479 | PM2.5 |
| 2016-08-31 | 170 | PM2.5 |
| 2020-09-16 | 162 | PM2.5 |
| 2020-09-17 | 160 | PM2.5 |
| 2016-08-28 | 159 | PM2.5 |
The air on a normal day
Across 3,652 monitored days from 2016 to 2025, the air in Gallatin County rated Good on 82% of them, more often than the 72% typical of monitored counties, and Moderate on 17%. The median day sat at AQI 29; one day in ten went above 56.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)93%3,400 days
- nitrogen dioxide5%179 days
- carbon monoxide2%73 days
Gallatin County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 358 | 7 | 0 | 0 | 11 | 70 |
| 2024 | 365 | 329 | 36 | 0 | 0 | 18 | 84 |
| 2023 | 365 | 331 | 34 | 0 | 0 | 26 | 98 |
| 2022 | 365 | 290 | 71 | 4 | 0 | 32 | 148 |
| 2021 | 365 | 243 | 108 | 14 | 1 | 41 | 158 |
| 2020 | 366 | 290 | 65 | 11 | 2 | 29 | 162 |
| 2019 | 365 | 301 | 64 | 0 | 0 | 33 | 92 |
| 2018 | 365 | 289 | 70 | 6 | 1 | 32 | 154 |
| 2017 | 365 | 263 | 99 | 3 | 1 | 31 | 152 |
| 2016 | 366 | 298 | 58 | 10 | 4 | 32 | 479 |
| 2015 | 365 | 284 | 77 | 4 | 1 | 29 | 183 |
| 2014 | 365 | 287 | 78 | 0 | 0 | 33 | 87 |
| 2013 | 365 | 294 | 71 | 0 | 0 | 32 | 79 |
| 2012 | 366 | 272 | 86 | 8 | 0 | 33 | 138 |
| 2011 | 365 | 204 | 160 | 1 | 0 | 47 | 103 |
| 2010 | 365 | 239 | 124 | 2 | 0 | 38 | 124 |
*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
- Silver Bow County7/yr
- Sanders County7/yr
- Powder River County6/yr
- Flathead County6/yr
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.