Daily Air Quality Index summaries from EPA monitors in Umatilla, Oregon, 1983–2025.
71%
Good days in 2025
41
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 Umatilla, Oregon on 365 days. 260 of those days (71%) were in the Good range, and the median daily AQI was 41. That median is higher than the typical monitored county in Oregon (median 29 across 21 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 261 days. Across the years with fuller monitoring, the share of Good days fell: an average of 79% in 1986–1993 versus 72% in 2023–2025.
Years with fewer than 120 monitored days (1987, 1988, 1989, 1990, 1991, 2003…) 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)
261
72%
Ozone
104
28%
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
260
105
0
0
0
0
41
64
95
PM2.5
2024
366
272
90
4
0
0
0
38
63
117
PM2.5
2023
365
259
103
0
1
2
0
42
61
267
PM2.5
2022
365
244
118
3
0
0
0
39
66
141
PM2.5
2021
365
265
92
6
2
0
0
38
64
169
PM2.5
2020
366
273
85
0
1
2
5
38
60
738
PM2.5
2019
365
267
97
1
0
0
0
40
63
104
PM2.5
2018
333
257
68
5
2
1
0
36
64
254
PM2.5
2017
365
222
131
9
1
2
0
44
70
252
PM2.5
2016
366
297
68
1
0
0
0
35
58
112
PM2.5
2015
365
246
110
6
3
0
0
41
63
160
PM2.5
2014
361
273
88
0
0
0
0
37
64
99
PM2.5
2013
364
220
138
6
0
0
0
45
68
115
PM2.5
2012
365
244
119
2
0
0
0
42
64
108
PM2.5
2011
362
274
87
1
0
0
0
39
66
104
PM2.5
2010
365
245
120
0
0
0
0
40
65
93
PM2.5
2009
365
234
130
1
0
0
0
42
70
103
PM2.5
2008
364
237
120
7
0
0
0
42
74
124
PM2.5
2007
363
239
122
1
1
0
0
44
71
155
Ozone
2006
361
267
94
0
0
0
0
29
66
93
PM2.5
2005
362
257
101
4
0
0
0
28
74
138
PM2.5
2004
358
235
116
6
1
0
0
34
77
153
PM2.5
2003
84
72
11
1
0
0
0
23
56
109
PM2.5
2002
321
223
90
8
0
0
0
33
72
140
PM2.5
2001
324
229
94
1
0
0
0
32
66
112
PM2.5
2000
341
236
99
6
0
0
0
36
69
117
PM2.5
1999
175
120
54
1
0
0
0
34
67
146
PM2.5
1998
207
202
5
0
0
0
0
18
39
67
PM10
1997
227
221
6
0
0
0
0
20
42
58
PM10
1996
203
195
8
0
0
0
0
20
42
66
PM10
1995
211
197
14
0
0
0
0
22
45
67
PM10
1994
206
187
19
0
0
0
0
25
50
73
PM10
1993
194
140
52
1
1
0
0
34
63
190
PM10
1992
204
170
34
0
0
0
0
31
57
90
PM10
1991
115
86
27
2
0
0
0
31
66
134
PM10
1990
55
47
8
0
0
0
0
29
56
71
PM10
1989
58
48
10
0
0
0
0
31
56
74
PM10
1988
57
41
16
0
0
0
0
33
65
83
PM10
1987
62
42
20
0
0
0
0
39
66
91
PM10
1986
153
123
30
0
0
0
0
31
56
90
PM10
1984
46
37
9
0
0
0
0
35
56
69
PM10
1983
12
10
2
0
0
0
0
37
51
60
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 Oregon with a similar median AQI in 2025
