Daily Air Quality Index summaries from EPA monitors in San Juan, Utah, 1988–2025.
76%
Good days in 2025
44
Median daily AQI, 2025
1
Days above 100 in 2025
361
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for San Juan, Utah on 361 days. 274 of those days (76%) were in the Good range, and the median daily AQI was 44. That median is about the same as the typical monitored county in Utah (median 45 across 15 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 359 days. Across the years with fuller monitoring, the share of Good days fell: an average of 84% in 1992–1994 versus 76% in 2023–2025.
Years with fewer than 120 monitored days (1988, 1989, 1990, 1991) 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
359
99%
Fine particles (PM2.5)
2
1%
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
361
274
86
1
0
0
0
44
61
108
Ozone
2024
356
276
77
3
0
0
0
44
64
126
Ozone
2023
357
267
90
0
0
0
0
45
61
87
Ozone
2022
365
306
59
0
0
0
0
44
58
87
Ozone
2021
364
276
86
2
0
0
0
44
67
115
Ozone
2020
363
294
67
2
0
0
0
43
58
119
Ozone
2019
363
286
70
3
1
3
0
44
58
268
Ozone
2018
356
245
104
7
0
0
0
44
77
119
Ozone
2017
351
263
88
0
0
0
0
44
61
100
Ozone
2016
365
309
56
0
0
0
0
44
54
93
Ozone
2015
362
285
76
1
0
0
0
43
64
105
Ozone
2014
355
278
77
0
0
0
0
44
61
100
Ozone
2013
343
269
74
0
0
0
0
44
64
97
Ozone
2012
365
238
122
5
0
0
0
46
77
129
Ozone
2011
354
236
115
3
0
0
0
47
71
108
Ozone
2010
354
244
108
2
0
0
0
47
67
119
Ozone
2009
340
215
123
2
0
0
0
48
64
112
Ozone
2008
358
229
125
4
0
0
0
48
74
115
Ozone
2007
351
225
120
6
0
0
0
45
74
112
Ozone
2006
361
224
135
2
0
0
0
47
77
108
Ozone
2005
338
236
98
4
0
0
0
46
77
126
Ozone
2004
358
233
119
6
0
0
0
47
74
122
Ozone
2003
336
181
147
8
0
0
0
49
87
122
Ozone
2002
355
200
148
7
0
0
0
48
84
115
Ozone
2001
346
272
73
1
0
0
0
43
61
101
Ozone
2000
344
223
110
11
0
0
0
45
77
129
Ozone
1999
331
197
129
5
0
0
0
48
84
133
Ozone
1998
353
205
144
4
0
0
0
48
80
119
Ozone
1997
329
245
83
1
0
0
0
44
67
101
Ozone
1996
334
206
121
7
0
0
0
47
84
129
Ozone
1995
307
247
58
2
0
0
0
44
61
133
Ozone
1994
342
240
101
1
0
0
0
46
67
101
Ozone
1993
339
299
40
0
0
0
0
44
54
87
Ozone
1992
182
173
9
0
0
0
0
35
48
67
Ozone
1991
99
98
1
0
0
0
0
21
33
57
PM2.5
1990
91
91
0
0
0
0
0
21
32
49
PM2.5
1989
86
86
0
0
0
0
0
21
35
49
PM2.5
1988
73
73
0
0
0
0
0
18
32
42
PM2.5
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 Utah with a similar median AQI in 2025
