Bad Air Days in Ada County, Idaho: 12 a Year
12 bad air days a year
Among the worst tenth of monitored US counties. Ranked 69 of 996 monitored counties, where 1 is worst.
What makes them bad: a mix of particles and ozone (59% particle days).
When the bad days come in Ada
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in August and July and September. Averaged over 2016 to 2025.
Is a purifier worth it 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.
- Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Better or worse than it was
In 2000 to 2009 this county averaged 12 bad days a year; in 2016 to 2025, 12. Not much has changed. The worst recent year was 2024, with 35 bad days on 366 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2024-07-23 | 214 | Ozone |
| 2020-09-13 | 198 | PM2.5 |
| 2017-09-06 | 196 | PM2.5 |
| 2024-08-08 | 181 | PM2.5 |
| 2024-08-31 | 180 | PM2.5 |
The air on a normal day
Across 3,653 monitored days from 2016 to 2025, the air in Ada County rated Good on 67% of them, less often than the 72% typical of monitored counties, and Moderate on 30%. The median day sat at AQI 44; one day in ten went above 74.
The pollutant setting the AQI on an ordinary day here:
- ozone59%2,150 days
- fine particles (PM2.5)38%1,397 days
- nitrogen dioxide2%72 days
- coarse dust (PM10)1%29 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 270 | 95 | 0 | 0 | 42 | 97 |
| 2024 | 366 | 230 | 101 | 35 | 7 | 44 | 214 |
| 2023 | 365 | 251 | 111 | 3 | 0 | 44 | 120 |
| 2022 | 365 | 196 | 162 | 7 | 1 | 48 | 166 |
| 2021 | 365 | 223 | 124 | 18 | 3 | 46 | 173 |
| 2020 | 366 | 242 | 106 | 18 | 7 | 44 | 198 |
| 2019 | 365 | 266 | 99 | 0 | 0 | 41 | 100 |
| 2018 | 365 | 266 | 92 | 7 | 0 | 42 | 134 |
| 2017 | 365 | 217 | 126 | 22 | 4 | 46 | 196 |
| 2016 | 366 | 271 | 88 | 7 | 0 | 41 | 116 |
| 2015 | 365 | 276 | 80 | 9 | 2 | 41 | 172 |
| 2014 | 365 | 277 | 87 | 1 | 1 | 41 | 152 |
| 2013 | 365 | 268 | 82 | 15 | 4 | 38 | 194 |
| 2012 | 366 | 265 | 90 | 11 | 2 | 41 | 215 |
| 2011 | 365 | 276 | 84 | 5 | 0 | 43 | 115 |
| 2010 | 365 | 102 | 259 | 4 | 0 | 55 | 136 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Lemhi County15/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, and on why a purifier does not touch ozone in smoke vs ozone.