Daily Air Quality Index summaries from EPA monitors in Box Elder, Utah, 1985–2025.
65%
Good days in 2025
45
Median daily AQI, 2025
1
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 Box Elder, Utah on 365 days. 236 of those days (65%) were in the Good range, and the median daily AQI was 45. 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 303 days. Across the years with fuller monitoring, the share of Good days rose: an average of 43% in 2001–2003 versus 69% in 2023–2025.
Years with fewer than 120 monitored days (1985, 2000) 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
303
83%
Fine particles (PM2.5)
52
14%
Nitrogen dioxide (NO₂)
5
1%
Coarse particles (PM10)
5
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
365
236
128
1
0
0
0
45
67
105
Ozone
2024
366
214
147
5
0
0
0
47
80
133
Ozone
2023
360
302
58
0
0
0
0
38
54
96
Ozone
2022
281
266
15
0
0
0
0
35
47
90
Ozone
2021
363
281
78
4
0
0
0
42
67
119
Ozone
2020
355
316
36
3
0
0
0
40
51
147
Ozone
2019
364
300
62
2
0
0
0
41
54
121
Ozone
2018
365
201
155
8
1
0
0
48
84
151
Ozone
2017
365
207
147
10
1
0
0
48
80
154
Ozone
2016
366
269
93
4
0
0
0
41
70
120
Ozone
2015
365
249
111
5
0
0
0
45
71
120
Ozone
2014
365
256
103
5
1
0
0
45
67
156
Ozone
2013
365
200
143
20
2
0
0
49
90
153
Ozone
2012
366
212
140
14
0
0
0
48
85
126
Ozone
2011
365
219
138
4
4
0
0
47
77
160
Ozone
2010
364
221
132
11
0
0
0
47
77
142
Ozone
2009
239
129
105
5
0
0
0
49
84
132
Ozone
2008
232
117
103
12
0
0
0
50
90
129
Ozone
2007
242
92
131
18
1
0
0
58
97
157
Ozone
2006
223
102
105
16
0
0
0
54
90
147
Ozone
2005
304
194
90
18
2
0
0
46
84
159
Ozone
2004
280
174
99
5
2
0
0
47
80
159
Ozone
2003
223
106
101
15
1
0
0
51
97
185
Ozone
2002
224
98
92
29
5
0
0
58
112
174
Ozone
2001
218
85
109
21
3
0
0
58
105
159
Ozone
2000
43
31
11
1
0
0
0
33
74
101
PM2.5
1985
1
1
0
0
0
0
0
42
42
42
Ozone
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
