Best Cities for Air Quality in Idaho
Ranking of cities with the cleanest air in Idaho based on AQI data.
Cleanest air in Idaho: Boise
Of the 1 Idaho metro area EPA published a full year of AQI data for in 2025, Boise recorded the highest share of Good-air days: 182 of 365 monitored days (49.9%) at AQI 50 or below, with a median AQI of 51 and 1 day above AQI 100. Its peak reading that year was AQI 135. The pollutant that set the daily AQI most often was fine particulate matter (PM2.5) (206 days).
| # | City (EPA area) | Good days (2025) | Median AQI | Days over 100 | Peak AQI | AQI now |
|---|---|---|---|---|---|---|
| 1 | BoiseBoise City, ID | 182 / 365 (49.9%) | 51 | 1 | 135 | 38 |
Figures are EPA's published annual AQI summaries by metropolitan area (Annual AQI by CBSA, 2019–2025), retrieved 2026-09-07. The daily AQI EPA summarises is the highest value any monitor in the area reported that day, so these are metro-area readings, not statewide or rural ones.
Boise's air quality year by year
One clean year can be luck — a mild summer, no wildfire smoke. This is every year EPA has published for the Boise City, ID area, so you can see whether Boise's ranking is durable.
| Year | Days measured | Good days | Median AQI | Days over 100 | Days over 150 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|---|---|
| 2019 | 365 | 176 | 51 | 3 | 1 | 170 | fine particulate matter (PM2.5) |
| 2020 | 366 | 142 | 54 | 21 | 11 | 223 | fine particulate matter (PM2.5) |
| 2021 | 365 | 131 | 54 | 20 | 4 | 173 | fine particulate matter (PM2.5) |
| 2022 | 365 | 132 | 55 | 13 | 2 | 188 | fine particulate matter (PM2.5) |
| 2023 | 365 | 180 | 51 | 3 | 0 | 120 | fine particulate matter (PM2.5) |
| 2024 | 366 | 147 | 54 | 68 | 35 | 265 | fine particulate matter (PM2.5) |
| 2025 | 365 | 182 | 51 | 1 | 0 | 135 | fine particulate matter (PM2.5) |
Across 2019–2025, Boise's air worsened: the area's median AQI held near 53 and days above AQI 100 rose from about 15 to 24 per year (comparing the earlier and later halves of the period).
How Idaho compares
Ranked by the median of its metro areas' median AQI in 2025, Idaho is #34 cleanest of the 51 states EPA publishes metro AQI data for, at a median AQI of 51. The cleanest state on that measure is Alaska; the most polluted is Arizona. See the full state air quality rankings.
What this ranking does and does not cover
We track 1 Idaho city. 1 has a full 2025 EPA record and is ranked above.
EPA's AQI is reported by metropolitan area, and the daily value is the worst reading from any monitor in that area. Rural Idaho — and any town without a regulatory monitor — is not represented here. A high Good-day share means the monitored metro air was clean on most days; it is not a statement about a specific street, and it does not capture short pollution spikes between the daily summaries.