Daily Air Quality Index summaries from EPA monitors in Linn, Oregon, 1985–2025.
80%
Good days in 2025
27
Median daily AQI, 2025
1
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 Linn, Oregon on 365 days. 292 of those days (80%) were in the Good range, and the median daily AQI was 27. That median is about the same as the typical monitored county in Oregon (median 29 across 21 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 365 days. Across the years with fuller monitoring, the share of Good days rose: an average of 71% in 2001–2004 versus 81% in 2023–2025.
Years with fewer than 120 monitored days (1990, 1991, 1992, 1999, 2000, 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)
365
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
365
292
72
1
0
0
0
27
57
122
PM2.5
2024
366
320
46
0
0
0
0
25
52
86
PM2.5
2023
365
278
83
4
0
0
0
34
62
125
PM2.5
2022
365
254
109
2
0
0
0
33
65
127
PM2.5
2021
365
268
96
1
0
0
0
34
61
136
PM2.5
2020
366
245
110
0
0
3
8
36
67
853
PM2.5
2019
365
233
130
2
0
0
0
37
66
104
PM2.5
2018
365
254
106
5
0
0
0
36
66
122
PM2.5
2017
365
254
102
4
5
0
0
32
65
186
PM2.5
2016
366
298
68
0
0
0
0
26
56
80
PM2.5
2015
365
272
88
2
3
0
0
31
61
189
PM2.5
2014
365
276
87
2
0
0
0
33
59
130
PM2.5
2013
365
253
107
5
0
0
0
31
68
111
PM2.5
2012
366
285
81
0
0
0
0
31
58
92
PM2.5
2011
363
228
129
3
2
1
0
34
67
212
PM2.5
2010
365
225
140
0
0
0
0
34
66
89
PM2.5
2009
365
202
157
5
1
0
0
44
70
154
PM2.5
2008
366
199
162
5
0
0
0
45
73
122
PM2.5
2007
363
260
96
6
0
1
0
35
66
202
PM2.5
2006
362
281
81
0
0
0
0
26
59
87
PM2.5
2005
362
268
90
3
1
0
0
29
67
152
PM2.5
2004
265
176
82
7
0
0
0
37
71
125
PM2.5
2003
111
82
29
0
0
0
0
34
68
92
PM2.5
2002
175
130
43
2
0
0
0
39
64
110
PM2.5
2001
120
87
32
1
0
0
0
36
66
104
PM2.5
2000
115
81
32
2
0
0
0
34
75
122
PM2.5
1999
22
8
13
1
0
0
0
55
99
109
PM2.5
1992
4
4
0
0
0
0
0
43
46
46
PM10
1991
58
46
12
0
0
0
0
30
61
76
PM10
1990
59
52
7
0
0
0
0
29
51
66
PM10
1989
33
29
4
0
0
0
0
27
52
67
PM10
1988
56
44
12
0
0
0
0
32
57
67
PM10
1987
13
9
4
0
0
0
0
36
71
73
PM10
1986
36
26
10
0
0
0
0
42
64
87
PM10
1985
62
39
23
0
0
0
0
43
64
77
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
