Air Quality Rankings for Idaho 2026

Idaho has 20 cities with EPA air quality data. Custer, Idaho has the cleanest air with a 5-year average AQI of 8. Benewah, Idaho has the highest AQI at 48.

#	City	5yr Avg AQI	Current AQI	Worst Pollutant	Trend	Grade
1	Custer, Idaho	8	8	PM2.5	Stable	A
2	Jerome, Idaho	17	13	PM2.5	Improving	B
3	Latah, Idaho	18	22	PM2.5	Worsening	B
4	Blaine, Idaho	21	19	PM2.5	Worsening	C
5	Franklin, Idaho	25	24	PM2.5	Improving	B
6	Twin Falls, Idaho	27	25	PM2.5	Improving	B
7	Bonneville, Idaho	30	25	PM2.5	Improving	B
8	Kootenai, Idaho	30	32	PM2.5	Improving	B
9	Nez Perce, Idaho	33	36	PM2.5	Worsening	C
10	Bonner, Idaho	33	34	PM2.5	Worsening	C
11	Valley, Idaho	37	36	PM2.5	Worsening	D
12	Bannock, Idaho	37	41	PM2.5	Worsening	C
13	Lemhi, Idaho	40	32	PM2.5	Improving	B
14	Canyon, Idaho	41	34	PM2.5	Worsening	C
15	Butte, Idaho	42	44	Ozone	Worsening	C
16	Idaho, Idaho	42	44	PM2.5	Worsening	C
17	Boise, Idaho	43	39	PM2.5	Stable	C
18	Shoshone, Idaho	43	47	PM2.5	Improving	B
19	Ada, Idaho	45	44	Ozone	Worsening	C
20	Benewah, Idaho	48	48	PM2.5	Stable	C

Air quality data for Idaho is sourced from the EPA Air Quality System (AQS), which monitors outdoor air quality at thousands of stations nationwide.
— EPA Air Quality System

Frequently Asked Questions

Custer, Idaho has the best air quality in Idaho with a 5-year average AQI of 8 and a grade of A.

Idaho has 20 cities with EPA air quality monitoring data in our database, covering multiple years of AQI measurements.

The Air Quality Index (AQI) measures five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Lower AQI values indicate cleaner air — 0-50 is "Good," while 150+ is "Unhealthy."

Sources: EPA Air Quality System (AQS)

Cities ranked by 5-year average AQI (lower is better). Grades factor in average AQI, trend direction, unhealthy days, and dominant pollutant.

Cleanest Cities Nationwide →All Air Quality in Idaho →