Daily Air Quality Index summaries from EPA monitors in Sanders, Montana, 1985–2025.
82%
Good days in 2025
16
Median daily AQI, 2025
0
Days above 100 in 2025
345
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Sanders, Montana on 345 days. 283 of those days (82%) were in the Good range, and the median daily AQI was 16. That median is lower than the typical monitored county in Montana (median 25.5 across 18 counties), and lower than the typical monitored U.S. county (40). The main pollutant was coarse particles (PM10) on 326 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 84% in 1988–1990 versus 82% in 2023–2025.
Years with fewer than 120 monitored days (1994, 1995, 1996, 1997, 1998, 1999…) 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
Coarse particles (PM10)
326
94%
Fine particles (PM2.5)
19
6%
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
345
283
62
0
0
0
0
16
55
85
PM10
2024
364
339
25
0
0
0
0
21
44
69
PM10
2023
364
263
96
3
2
0
0
37
58
181
PM2.5
2022
365
266
94
2
3
0
0
36
59
188
PM2.5
2021
356
232
104
8
11
1
0
42
84
207
PM2.5
2020
366
302
56
1
4
3
0
31
57
261
PM2.5
2019
365
289
76
0
0
0
0
33
56
95
PM2.5
2018
365
256
95
14
0
0
0
37
73
148
PM2.5
2017
358
242
103
6
2
4
1
33
75
449
PM2.5
2016
335
324
11
0
0
0
0
12
26
91
PM10
2015
362
336
23
3
0
0
0
17
39
150
PM10
2014
335
326
9
0
0
0
0
13
28
89
PM10
2013
174
166
7
1
0
0
0
13
32
106
PM2.5
2012
120
114
6
0
0
0
0
11
33
86
PM2.5
2011
121
113
8
0
0
0
0
21
39
62
PM2.5
2010
122
105
17
0
0
0
0
31
52
70
PM2.5
2009
121
106
15
0
0
0
0
28
53
75
PM2.5
2008
122
97
24
1
0
0
0
29
56
113
PM2.5
2007
121
91
29
0
1
0
0
34
56
165
PM2.5
2006
122
98
24
0
0
0
0
33
59
82
PM2.5
2005
122
102
20
0
0
0
0
29
53
66
PM2.5
2004
122
96
26
0
0
0
0
28
55
74
PM2.5
2003
123
99
23
1
0
0
0
28
57
104
PM2.5
2002
122
101
21
0
0
0
0
29
55
76
PM2.5
2001
123
105
17
1
0
0
0
26
56
120
PM2.5
2000
151
124
27
0
0
0
0
27
57
93
PM2.5
1999
92
91
1
0
0
0
0
11
32
55
PM10
1998
116
112
4
0
0
0
0
16
35
59
PM10
1997
113
109
4
0
0
0
0
18
33
68
PM10
1996
110
99
11
0
0
0
0
19
51
98
PM10
1995
118
107
11
0
0
0
0
23
49
75
PM10
1994
112
96
16
0
0
0
0
24
54
93
PM10
1993
106
89
17
0
0
0
0
30
54
79
PM10
1992
224
193
31
0
0
0
0
26
55
98
PM10
1991
354
318
31
5
0
0
0
24
51
143
PM10
1990
338
276
54
7
1
0
0
28
64
154
PM10
1989
340
290
49
1
0
0
0
27
56
133
PM10
1988
247
208
38
1
0
0
0
30
58
103
PM10
1987
75
51
24
0
0
0
0
39
68
87
PM10
1986
46
29
17
0
0
0
0
45
65
80
PM10
1985
26
19
7
0
0
0
0
44
65
68
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 Montana with a similar median AQI in 2025
