Walla Walla County, Washington air quality history
Daily Air Quality Index summaries from EPA monitors in Walla Walla, Washington, 1986–2025.
81%
Good days in 2025
28
Median daily AQI, 2025
0
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Walla Walla, Washington on 365 days. 295 of those days (81%) were in the Good range, and the median daily AQI was 28. That median is about the same as the typical monitored county in Washington (median 28 across 30 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 251 days. Across the years with fuller monitoring, the share of Good days rose: an average of 61% in 1986–1988 versus 83% in 2023–2025.
Years with fewer than 120 monitored days (1996, 1997, 1998, 1999, 2000, 2001…) 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)
251
69%
Coarse particles (PM10)
114
31%
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
365
295
70
0
0
0
0
28
56
85
PM2.5
2024
366
314
52
0
0
0
0
24
54
87
PM2.5
2023
365
300
61
1
1
1
1
28
55
305
PM2.5
2022
365
292
70
2
1
0
0
25
59
152
PM2.5
2021
365
309
51
3
2
0
0
24
55
172
PM2.5
2020
366
297
60
0
1
2
6
26
55
855
PM2.5
2019
365
299
66
0
0
0
0
23
56
94
PM2.5
2018
365
292
65
5
2
1
0
26
61
242
PM2.5
2017
351
274
66
8
1
2
0
23
64
222
PM2.5
2016
271
229
42
0
0
0
0
24
54
85
PM2.5
2015
362
289
69
3
1
0
0
26
56
153
PM2.5
2014
319
288
31
0
0
0
0
22
50
71
PM2.5
2013
350
275
73
2
0
0
0
28
59
104
PM2.5
2012
363
298
65
0
0
0
0
24
55
93
PM2.5
2011
363
302
61
0
0
0
0
26
57
86
PM2.5
2010
365
284
81
0
0
0
0
29
57
79
PM2.5
2009
365
276
89
0
0
0
0
35
58
82
PM2.5
2008
366
267
98
1
0
0
0
33
64
107
PM2.5
2007
365
267
97
1
0
0
0
31
65
108
PM2.5
2006
365
257
106
2
0
0
0
35
65
126
PM2.5
2005
365
271
92
2
0
0
0
31
63
125
PM2.5
2004
366
236
125
4
1
0
0
41
66
173
PM2.5
2003
362
229
130
1
1
0
1
38
66
1316
PM2.5
2002
187
121
61
5
0
0
0
34
69
122
PM2.5
2001
117
100
16
1
0
0
0
26
53
114
PM10
2000
119
107
11
1
0
0
0
20
54
131
PM10
1999
113
92
20
0
1
0
0
23
55
172
PM10
1998
78
60
17
1
0
0
0
23
64
131
PM10
1997
64
51
10
3
0
0
0
29
69
128
PM10
1996
64
54
10
0
0
0
0
26
61
97
PM10
1995
67
58
9
0
0
0
0
21
53
75
PM10
1994
65
52
12
1
0
0
0
27
63
110
PM10
1993
74
59
14
1
0
0
0
25
56
121
PM10
1992
67
55
12
0
0
0
0
27
55
85
PM10
1991
60
41
15
2
1
0
1
32
83
663
PM10
1990
63
50
13
0
0
0
0
33
59
85
PM10
1989
62
50
11
1
0
0
0
30
54
129
PM10
1988
151
98
48
2
2
0
1
36
70
747
PM10
1987
154
91
58
4
1
0
0
40
83
164
PM10
1986
144
86
52
6
0
0
0
41
77
144
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
