Bad Air Days in Asotin County, Washington: 8 a Year

8 bad air days a year

More bad air days than three quarters of monitored counties. Ranked 114 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 and July. Averaged over 2016 to 2025.

What actually helps 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.

The worst days on file

The worst recent year was 2021, with 19 bad days on 335 monitored days.

Date	AQI	Main pollutant
2020-09-13	328	PM2.5
2017-09-05	274	PM2.5
2017-09-06	250	PM2.5
2020-09-14	244	PM2.5
2017-09-07	240	PM2.5

An ordinary day in Asotin

Across 3,516 monitored days from 2016 to 2025, the air in Asotin County rated Good on 63% of them, less often than the 72% typical of monitored counties, and Moderate on 35%. The median day sat at AQI 41; one day in ten went above 69.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%3,516 days

Asotin County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	362	224	135	3	1	42	151
2024	361	224	131	6	4	42	196
2023	359	184	169	6	2	49	204
2022	358	195	156	7	4	46	200
2021	335	176	140	19	5	48	233
2020	350	229	112	9	7	38	328
2019	357	250	106	1	0	36	125
2018	325	214	103	8	2	36	200
2017	347	226	102	19	8	39	274
2016	362	280	82	0	0	36	93
2015	267	177	90	0	0	36	84
2014	290	221	66	3	0	33	128
2013	323	202	121	0	0	42	98
2012	364	219	135	10	5	39	202
2011	361	304	57	0	0	27	74
2010	359	277	82	0	0	34	88

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

Washington compared

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.