Daily Air Quality Index summaries from EPA monitors in Plumas, California, 1986–2025.
53%
Good days in 2025
45
Median daily AQI, 2025
10
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 Plumas, California on 365 days. 193 of those days (53%) were in the Good range, and the median daily AQI was 45. That median is about the same as the typical monitored county in California (median 45.5 across 46 counties), and higher 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 fell: an average of 73% in 1987–1994 versus 52% in 2023–2025.
Years with fewer than 120 monitored days (1989, 1990, 1991, 1992, 2009, 2013…) 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
193
162
10
0
0
0
45
84
120
PM2.5
2024
366
188
162
7
7
2
0
48
88
253
PM2.5
2023
365
186
168
11
0
0
0
50
87
142
PM2.5
2022
359
148
182
25
4
0
0
55
96
175
PM2.5
2021
365
97
184
37
24
16
7
67
170
654
PM2.5
2020
360
135
175
16
17
10
7
56
146
755
PM2.5
2019
341
220
116
5
0
0
0
34
71
138
PM2.5
2018
350
186
154
8
2
0
0
47
85
162
PM2.5
2017
351
184
142
17
8
0
0
47
90
189
PM2.5
2016
355
203
141
10
1
0
0
43
76
152
PM2.5
2015
132
52
66
10
4
0
0
56
102
159
PM2.5
2014
127
58
56
10
3
0
0
52
103
158
PM2.5
2013
119
55
49
13
2
0
0
53
113
166
PM2.5
2012
124
67
49
8
0
0
0
48
92
124
PM2.5
2011
122
61
56
4
1
0
0
51
89
153
PM2.5
2010
124
70
51
3
0
0
0
44
78
110
PM2.5
2009
119
55
60
4
0
0
0
53
84
140
PM2.5
2008
141
60
71
4
4
2
0
55
93
218
PM2.5
2007
137
56
74
6
1
0
0
56
88
163
PM2.5
2006
365
264
98
3
0
0
0
40
71
139
Ozone
2005
363
257
104
0
2
0
0
41
68
186
Ozone
2004
366
282
81
3
0
0
0
42
73
124
Ozone
2003
355
264
84
7
0
0
0
42
73
144
Ozone
2002
363
163
155
45
0
0
0
56
105
147
Ozone
2001
365
274
80
10
1
0
0
36
73
153
Ozone
2000
365
272
85
8
0
0
0
42
71
127
Ozone
1999
360
221
125
10
4
0
0
48
84
177
Ozone
1998
327
243
82
2
0
0
0
43
71
112
Ozone
1997
352
347
5
0
0
0
0
13
31
56
PM10
1996
262
183
74
5
0
0
0
44
74
133
Ozone
1995
259
150
87
21
1
0
0
49
97
177
Ozone
1994
248
130
93
25
0
0
0
48
101
143
Ozone
1993
255
173
79
3
0
0
0
46
71
119
Ozone
1992
87
77
10
0
0
0
0
26
52
83
PM10
1991
52
39
12
1
0
0
0
22
74
104
PM10
1990
56
46
10
0
0
0
0
24
74
92
PM10
1989
53
40
13
0
0
0
0
23
73
95
PM10
1988
45
33
12
0
0
0
0
30
89
100
PM10
1987
182
178
4
0
0
0
0
11
19
82
NO2
1986
10
2
8
0
0
0
0
71
85
85
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 California with a similar median AQI in 2025
