Daily Air Quality Index summaries from EPA monitors in San Miguel, Colorado, 1985–2025.
83%
Good days in 2025
36
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 San Miguel, Colorado on 365 days. 303 of those days (83%) were in the Good range, and the median daily AQI was 36. That median is lower than the typical monitored county in Colorado (median 46 across 27 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 161 days. Across the years with fuller monitoring, the share of Good days rose: an average of 77% in 1986–1990 versus 81% in 2023–2025.
Years with fewer than 120 monitored days (2003, 2004, 2005, 2007, 2008, 2009…) 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
Ozone
161
44%
Fine particles (PM2.5)
160
44%
Coarse particles (PM10)
44
12%
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
303
62
0
0
0
0
36
60
94
Ozone
2024
361
311
50
0
0
0
0
19
54
97
PM10
2023
253
185
68
0
0
0
0
47
61
84
Ozone
2022
255
194
60
1
0
0
0
45
64
108
Ozone
2021
252
165
87
0
0
0
0
48
67
97
Ozone
2020
247
155
90
2
0
0
0
48
67
136
Ozone
2019
241
189
52
0
0
0
0
45
58
87
Ozone
2018
238
160
76
2
0
0
0
46
71
101
Ozone
2017
229
197
32
0
0
0
0
43
54
87
Ozone
2016
245
189
55
1
0
0
0
44
63
105
Ozone
2015
236
188
47
1
0
0
0
44
58
105
Ozone
2014
274
205
69
0
0
0
0
45
64
93
Ozone
2013
262
173
87
1
1
0
0
47
74
156
Ozone
2012
209
163
45
1
0
0
0
44
61
119
Ozone
2011
246
142
102
2
0
0
0
48
74
101
Ozone
2010
147
129
17
0
1
0
0
19
54
200
PM10
2009
114
110
4
0
0
0
0
12
32
88
PM10
2008
112
105
7
0
0
0
0
14
32
64
PM10
2007
114
112
2
0
0
0
0
17
31
62
PM10
2006
121
119
2
0
0
0
0
19
35
64
PM10
2005
119
116
3
0
0
0
0
21
41
61
PM10
2004
116
110
6
0
0
0
0
19
41
59
PM10
2003
119
115
4
0
0
0
0
23
39
72
PM10
2002
225
219
6
0
0
0
0
19
38
57
PM10
2001
255
251
3
1
0
0
0
17
33
129
PM10
2000
269
260
9
0
0
0
0
19
36
62
PM10
1999
311
303
7
1
0
0
0
20
34
135
PM10
1998
365
354
11
0
0
0
0
21
40
68
PM10
1997
339
318
21
0
0
0
0
22
47
71
PM10
1996
328
313
15
0
0
0
0
21
38
77
PM10
1995
320
280
40
0
0
0
0
25
55
83
PM10
1994
281
251
30
0
0
0
0
26
51
100
PM10
1993
330
263
67
0
0
0
0
31
58
91
PM10
1992
308
245
63
0
0
0
0
32
55
77
PM10
1991
289
238
51
0
0
0
0
28
56
77
PM10
1990
283
246
37
0
0
0
0
29
54
82
PM10
1989
267
235
32
0
0
0
0
30
52
75
PM10
1988
41
37
4
0
0
0
0
31
46
66
PM10
1987
92
54
38
0
0
0
0
46
78
91
PM10
1986
338
187
135
16
0
0
0
47
80
130
PM10
1985
55
34
17
4
0
0
0
34
91
133
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 Colorado with a similar median AQI in 2025
