Daily Air Quality Index summaries from EPA monitors in Klamath, Oregon, 1986–2025.
64%
Good days in 2025
38
Median daily AQI, 2025
3
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 Klamath, Oregon on 365 days. 235 of those days (64%) were in the Good range, and the median daily AQI was 38. 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 365 days. Across the years with fuller monitoring, the share of Good days rose: an average of 54% in 1988–1990 versus 65% in 2023–2025.
Years with fewer than 120 monitored days (1986, 1987) 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
235
127
3
0
0
0
38
69
149
PM2.5
2024
366
259
91
9
6
1
0
33
76
207
PM2.5
2023
365
216
137
7
5
0
0
39
75
181
PM2.5
2022
365
222
139
2
2
0
0
38
70
163
PM2.5
2021
365
162
153
19
25
6
0
54
134
237
PM2.5
2020
366
172
148
23
20
1
2
52
124
763
PM2.5
2019
365
230
129
6
0
0
0
39
78
126
PM2.5
2018
360
184
136
12
20
8
0
49
114
249
PM2.5
2017
361
215
120
15
10
1
0
39
92
279
PM2.5
2016
363
250
113
0
0
0
0
41
67
92
PM2.5
2015
365
213
139
11
1
1
0
42
77
205
PM2.5
2014
365
222
139
4
0
0
0
42
72
136
PM2.5
2013
364
178
160
22
4
0
0
51
91
168
PM2.5
2012
360
216
135
8
1
0
0
39
81
152
PM2.5
2011
360
221
125
14
0
0
0
36
82
130
PM2.5
2010
363
229
130
4
0
0
0
35
70
143
PM2.5
2009
364
174
180
6
3
1
0
52
82
203
PM2.5
2008
364
107
222
30
5
0
0
59
99
164
PM2.5
2007
363
194
143
22
4
0
0
48
94
154
PM2.5
2006
364
178
160
18
8
0
0
51
93
184
PM2.5
2005
362
207
133
22
0
0
0
43
82
149
PM2.5
2004
366
237
108
18
3
0
0
37
88
162
PM2.5
2003
238
195
41
2
0
0
0
23
64
146
CO
2002
360
198
120
24
16
2
0
43
114
230
PM2.5
2001
349
252
91
6
0
0
0
33
68
111
PM2.5
2000
355
248
98
8
1
0
0
34
74
156
PM2.5
1999
266
187
74
5
0
0
0
33
74
141
PM2.5
1998
250
238
12
0
0
0
0
21
41
74
CO
1997
253
233
20
0
0
0
0
26
47
66
CO
1996
255
231
24
0
0
0
0
24
50
77
CO
1995
255
246
9
0
0
0
0
25
44
60
PM10
1994
261
210
51
0
0
0
0
28
57
75
PM10
1993
249
188
61
0
0
0
0
31
69
92
PM10
1992
263
198
64
1
0
0
0
34
60
134
PM10
1991
251
171
72
8
0
0
0
35
73
147
PM10
1990
239
140
80
18
1
0
0
43
95
152
PM10
1989
245
119
80
36
7
3
0
51
125
290
PM10
1988
261
143
87
20
6
1
4
46
112
709
PM10
1987
113
54
42
11
6
0
0
52
114
188
PM10
1986
91
45
34
9
2
1
0
52
121
283
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
