Daily Air Quality Index summaries from EPA monitors in Marion, Oregon, 1980–2025.
80%
Good days in 2025
35
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 Marion, Oregon on 365 days. 292 of those days (80%) were in the Good range, and the median daily AQI was 35. That median is higher than 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 243 days. Across the years with fuller monitoring, the share of Good days fell: an average of 84% in 1980–1982 versus 78% in 2023–2025.
Years with fewer than 120 monitored days (1989, 1990) 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)
243
67%
Ozone
122
33%
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
73
0
0
0
0
35
58
85
PM2.5
2024
366
298
64
4
0
0
0
35
56
129
PM2.5
2023
365
268
93
4
0
0
0
38
65
128
PM2.5
2022
365
254
104
5
2
0
0
36
70
168
PM2.5
2021
363
280
83
0
0
0
0
36
60
93
PM2.5
2020
365
278
76
1
0
1
9
36
63
1272
PM2.5
2019
356
262
94
0
0
0
0
37
63
93
PM2.5
2018
361
271
84
6
0
0
0
35
61
125
PM2.5
2017
362
287
66
9
0
0
0
33
62
150
PM2.5
2016
361
304
57
0
0
0
0
33
56
97
PM2.5
2015
365
267
95
1
2
0
0
37
62
176
PM2.5
2014
365
287
77
0
1
0
0
34
61
155
PM2.5
2013
361
247
109
5
0
0
0
37
69
123
PM2.5
2012
364
285
79
0
0
0
0
33
59
93
PM2.5
2011
365
277
88
0
0
0
0
34
65
96
PM2.5
2010
365
291
73
1
0
0
0
31
57
126
PM2.5
2009
361
261
99
1
0
0
0
36
69
140
PM2.5
2008
356
271
83
2
0
0
0
34
63
150
PM2.5
2007
365
280
79
6
0
0
0
31
65
115
PM2.5
2006
363
270
86
6
1
0
0
34
67
154
PM2.5
2005
365
260
98
7
0
0
0
35
67
133
PM2.5
2004
366
276
88
2
0
0
0
33
65
115
PM2.5
2003
327
296
25
6
0
0
0
30
50
133
CO
2002
338
292
43
3
0
0
0
32
54
109
Ozone
2001
335
288
46
1
0
0
0
31
54
134
Ozone
2000
345
286
59
0
0
0
0
31
58
96
Ozone
1999
362
295
64
3
0
0
0
33
58
112
PM2.5
1998
323
304
13
5
1
0
0
31
47
182
CO
1997
332
308
24
0
0
0
0
31
47
90
CO
1996
321
279
25
11
6
0
0
32
64
197
CO
1995
280
245
32
3
0
0
0
33
52
105
CO
1994
180
139
41
0
0
0
0
33
63
96
CO
1993
183
147
34
2
0
0
0
35
59
106
CO
1992
130
77
53
0
0
0
0
45
71
93
CO
1991
181
108
72
1
0
0
0
45
69
106
CO
1990
118
87
31
0
0
0
0
39
64
85
CO
1989
110
101
9
0
0
0
0
22
48
65
CO
1988
364
345
19
0
0
0
0
18
44
77
CO
1987
359
302
53
4
0
0
0
27
60
147
CO
1986
364
318
40
5
1
0
0
27
56
164
CO
1985
359
296
54
6
3
0
0
34
69
170
CO
1984
364
332
28
2
2
0
0
31
49
156
CO
1983
365
328
34
3
0
0
0
30
51
133
CO
1982
365
326
39
0
0
0
0
27
52
84
CO
1981
358
282
69
4
3
0
0
36
64
200
CO
1980
299
249
48
1
1
0
0
20
60
156
CO
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
