Daily Air Quality Index summaries from EPA monitors in Asotin, Washington, 1985–2025.
62%
Good days in 2025
42
Median daily AQI, 2025
3
Days above 100 in 2025
362
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Asotin, Washington on 362 days. 224 of those days (62%) were in the Good range, and the median daily AQI was 42. That median is higher than the typical monitored county in Washington (median 28 across 30 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 362 days. Across the years with fuller monitoring, the share of Good days fell: an average of 64% in 2007–2009 versus 58% in 2023–2025.
Years with fewer than 120 monitored days (2001, 2002, 2003, 2004, 2005, 2006…) are shown in the table but left out of comparisons and trend statements.
How the days broke down each year
Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Typical and high-end AQI over time
The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.
Median daily AQI
90th-percentile daily AQI
Main pollutant by day, 2025
On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.
Pollutant
Days as main pollutant
Share of monitored days
Fine particles (PM2.5)
362
100%
Year-by-year data
Annual AQI summary by year
Year
Days with AQI
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Median AQI
90th pct.
Max AQI
Main pollutant
2025
362
224
135
2
1
0
0
42
67
151
PM2.5
2024
361
224
131
2
4
0
0
42
69
196
PM2.5
2023
359
184
169
4
1
1
0
49
67
204
PM2.5
2022
358
195
156
3
4
0
0
46
72
200
PM2.5
2021
335
176
140
14
4
1
0
48
83
233
PM2.5
2020
350
229
112
2
1
5
1
38
66
328
PM2.5
2019
357
250
106
1
0
0
0
36
65
125
PM2.5
2018
325
214
103
6
2
0
0
36
72
200
PM2.5
2017
347
226
102
11
5
3
0
39
73
274
PM2.5
2016
362
280
82
0
0
0
0
36
57
93
PM2.5
2015
267
177
90
0
0
0
0
36
63
84
PM2.5
2014
290
221
66
3
0
0
0
33
61
128
PM2.5
2013
323
202
121
0
0
0
0
42
66
98
PM2.5
2012
364
219
135
5
4
1
0
39
67
202
PM2.5
2011
361
304
57
0
0
0
0
27
56
74
PM2.5
2010
359
277
82
0
0
0
0
34
58
88
PM2.5
2009
356
238
118
0
0
0
0
41
61
97
PM2.5
2008
359
233
126
0
0
0
0
40
67
92
PM2.5
2007
307
187
118
2
0
0
0
44
71
112
PM2.5
2006
54
52
2
0
0
0
0
22
36
62
PM10
2005
56
53
3
0
0
0
0
22
43
60
PM10
2004
55
54
1
0
0
0
0
20
39
74
PM10
2003
60
54
6
0
0
0
0
20
52
67
PM10
2002
60
56
4
0
0
0
0
20
47
85
PM10
2001
55
53
2
0
0
0
0
22
39
95
PM10
2000
59
56
3
0
0
0
0
22
49
74
PM10
1999
56
47
9
0
0
0
0
27
54
68
PM10
1998
56
49
7
0
0
0
0
23
55
67
PM10
1997
54
49
5
0
0
0
0
28
47
94
PM10
1996
56
52
4
0
0
0
0
26
49
71
PM10
1995
58
54
4
0
0
0
0
25
48
69
PM10
1994
58
44
14
0
0
0
0
29
59
66
PM10
1993
61
53
8
0
0
0
0
26
57
97
PM10
1992
60
58
2
0
0
0
0
27
43
55
PM10
1991
56
47
8
0
1
0
0
29
52
189
PM10
1990
55
50
5
0
0
0
0
27
50
83
PM10
1989
41
35
6
0
0
0
0
23
58
66
PM10
1988
43
33
10
0
0
0
0
30
65
87
PM10
1986
26
18
8
0
0
0
0
41
72
89
PM10
1985
5
3
2
0
0
0
0
35
80
80
PM10
What this data can and can’t tell you
It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.
It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.
Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.
Counties in Washington with a similar median AQI in 2025
