Bad Air Days in Bonneville County, Idaho: 2 a Year

2 bad air days a year

About the middle of monitored US counties. Ranked 462 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (100% particle days).

Which months to watch

Most bad days here fall in August and September. Averaged over 2016 to 2025.

Is a purifier worth it here?

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

Better or worse than it was

The worst recent year was 2021, with 9 bad days on 356 monitored days.

Date	AQI	Main pollutant
2020-08-20	155	PM2.5
2020-08-21	155	PM2.5
2020-08-22	155	PM2.5
2018-08-24	154	PM2.5
2020-08-23	151	PM2.5

Most days, not the worst ones

Across 3,537 monitored days from 2016 to 2025, the air in Bonneville County rated Good on 83% of them, more often than the 72% typical of monitored counties, and Moderate on 16%. The median day sat at AQI 30; one day in ten went above 54.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%3,537 days

Bonneville County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	359	334	25	0	0	22	95
2024	364	316	48	0	0	22	91
2023	348	326	22	0	0	25	84
2022	357	306	50	1	0	27	109
2021	356	275	72	9	0	31	144
2020	362	298	59	5	4	28	155
2019	357	287	70	0	0	38	67
2018	352	268	81	3	1	36	154
2017	358	277	77	4	0	32	149
2016	324	252	72	0	0	35	69
2015	104	92	12	0	0	23	63

*2025 may be a partial year in EPA's file.

Elsewhere in Idaho

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.