Bad Air Days in Lemhi County, Idaho: 15 a Year
15 bad air days a year
Among the worst tenth of monitored US counties. Ranked 50 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (100% particle days).
The bad-air season here
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in September and January and August and July. Averaged over 2016 to 2025.
What to buy, and what not to
- 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.
Better or worse than it was
In 2000 to 2009 this county averaged 9 bad days a year; in 2016 to 2025, 15. It has got worse. The worst recent year was 2017, with 31 bad days on 358 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2022-09-13 | 212 | PM2.5 |
| 2022-09-08 | 201 | PM2.5 |
| 2024-09-10 | 198 | PM2.5 |
| 2017-09-04 | 193 | PM2.5 |
| 2022-09-12 | 190 | PM2.5 |
The air on a normal day
Across 3,631 monitored days from 2016 to 2025, the air in Lemhi County rated Good on 59% of them, less often than the 72% typical of monitored counties, and Moderate on 36%. The median day sat at AQI 39; one day in ten went above 80.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)100%3,631 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 261 | 102 | 2 | 1 | 29 | 163 |
| 2024 | 366 | 207 | 143 | 16 | 4 | 37 | 198 |
| 2023 | 363 | 251 | 110 | 2 | 0 | 32 | 119 |
| 2022 | 365 | 199 | 136 | 30 | 12 | 44 | 212 |
| 2021 | 365 | 188 | 157 | 20 | 4 | 47 | 172 |
| 2020 | 365 | 194 | 160 | 11 | 3 | 46 | 168 |
| 2019 | 360 | 237 | 119 | 4 | 0 | 31 | 133 |
| 2018 | 360 | 225 | 132 | 3 | 0 | 38 | 121 |
| 2017 | 358 | 214 | 113 | 31 | 8 | 37 | 193 |
| 2016 | 364 | 182 | 153 | 29 | 3 | 51 | 160 |
| 2015 | 355 | 176 | 154 | 25 | 8 | 51 | 267 |
| 2014 | 348 | 171 | 160 | 17 | 1 | 52 | 157 |
| 2013 | 346 | 173 | 159 | 14 | 2 | 51 | 159 |
| 2012 | 362 | 164 | 152 | 46 | 30 | 54 | 289 |
| 2011 | 359 | 192 | 155 | 12 | 1 | 46 | 153 |
| 2010 | 343 | 199 | 130 | 14 | 1 | 43 | 154 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Ada County12/yr
- Benewah County10/yr
- Boise County10/yr
- Shoshone County8/yr
- Canyon County7/yr
- Nez Perce County7/yr
- Idaho County7/yr
- Bonner County7/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.