Smoke: keep one room clean
Shut the windows and run an air purifier sized for the room.
Wildfire smoke guide →Air quality in Idaho, county by county
19 Idaho counties have enough EPA monitor data to count bad-air days. Weighted by population, they averaged about 7 days a year from 2021 to 2025 when the air was unhealthy for sensitive groups or worse.
CDC's model, which estimates every county from monitors and satellites, gives the average Idaho county, weighted by population, about 5 smoky days (fine particles over 35.4 µg/m³, mostly wildfire smoke) and about 1 high-ozone day a year at its worst spot (2018 to 2022). See every county on the map.
Every Idaho county with monitors
Most bad-air days first. 7 have a full report. Compare with the worst and the cleanest counties in the US.
| County | Bad-air days a year | |
|---|---|---|
| Lemhi CountySmokeozone not measured | 14.0 | |
| Boise CountySmokeozone not measured | 13.2 | |
| Ada CountyBoise CityOzone and particles | 12.6 | |
| Idaho CountySummer smoke | 8.4 | |
| Nez Perce CountySmokeozone not measured | 7.8 | |
| Benewah CountySmokeozone not measured | 6.6 | |
| Canyon CountyNampaSmokeozone not measured | 6.4 | |
| Bonner CountySandpointSmokeozone not measured | 6.0 | |
| Shoshone CountySmokeozone not measured | 6.0 | |
| Valley CountySmokeozone not measured | 5.4 | |
| Kootenai CountyCoeur d'AleneSmokeozone not measured | 4.6 | |
| Boundary CountySmokeozone not measured | 4.3 | |
| Blaine CountyHaileySmokeozone not measured | 4.2 | |
| Latah CountyMoscowSmokeozone not measured | 3.8 | |
| Twin Falls CountyTwin FallsSmokeozone not measured | 3.4 | |
| Bannock CountyPocatelloSummer smoke | 3.0 | |
| Franklin CountyWinter particlesozone not measured | 2.2 | |
| Bonneville CountyIdaho FallsSmokeozone not measured | 2.0 | |
| Butte CountyOzone and particles | 0.6 | |
| No Idaho county with a monitor matches “”. Counties without a monitor aren't listed; a neighbor's numbers are a fair guide, or find it on the map. | ||
Counties without a monitor aren't listed. Air doesn't stop at the county line, so a neighbor's numbers are a fair guide.
What helps on a bad-air day
Check AirNow for today's reading and tomorrow's forecast, then match the step to the pollutant.
Upgrade the furnace filter
MERV 13 catches far more smoke than thin fiberglass filters.
Furnace filters →Questions people ask about air quality in Idaho
Which county in Idaho has the worst air?
Among Idaho counties with EPA monitors, Lemhi County had the most bad-air days from 2021 to 2025: about 14 bad-air days a year with an AQI over 100. That's about 1 day in 26.
How often is the air bad in Idaho?
Weighted by population, Idaho counties with monitors averaged about 7 bad-air days a year from 2021 to 2025 with an AQI over 100, when children, older adults and people with asthma should cut back outdoors. That's about 1 day in 49.
Which county in Idaho has the cleanest air?
Of the 19 counties with enough monitor data, Butte County had the fewest: 0.6 a year from 2021 to 2025. Counties without monitors aren't ranked.
Where can I check today's air quality in Idaho?
AirNow, run by the EPA and its partners, shows current readings and forecasts by ZIP code, and its fire and smoke map adds smoke plumes and low-cost sensors.
Sources: EPA AirData county AQI summaries, 2021 to 2025; CDC Environmental Public Health Tracking Network modeled PM2.5 and ozone, 2018 to 2022. Updated November 8, 2026.