Daily Air Quality Index summaries from EPA monitors in Twin Falls, Idaho, 1986–2025.
93%
Good days in 2025
26
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 Twin Falls, Idaho on 365 days. 339 of those days (93%) were in the Good range, and the median daily AQI was 26. That median is lower than the typical monitored county in Idaho (median 35 across 18 counties), and lower 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 rose: an average of 79% in 2001–2004 versus 88% in 2023–2025.
Years with fewer than 120 monitored days (1996, 1997, 1998, 1999, 2000, 2003…) 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
339
25
1
0
0
0
26
47
105
PM2.5
2024
347
264
76
4
3
0
0
23
64
158
PM2.5
2023
344
328
16
0
0
0
0
25
42
80
PM2.5
2022
353
280
71
1
1
0
0
31
55
155
PM2.5
2021
361
298
56
7
0
0
0
28
61
144
PM2.5
2020
364
313
44
3
4
0
0
24
56
163
PM2.5
2019
365
344
21
0
0
0
0
26
43
74
PM2.5
2018
355
271
79
3
2
0
0
39
60
151
PM2.5
2017
288
168
114
5
1
0
0
46
69
154
PM2.5
2016
352
333
19
0
0
0
0
22
42
69
PM2.5
2015
275
237
35
3
0
0
0
32
53
141
PM2.5
2013
305
277
28
0
0
0
0
18
49
88
PM2.5
2012
355
298
54
2
1
0
0
28
57
156
PM2.5
2011
350
311
39
0
0
0
0
30
52
70
PM2.5
2010
351
309
41
1
0
0
0
32
51
131
PM2.5
2009
358
289
68
1
0
0
0
36
55
124
PM2.5
2008
335
264
71
0
0
0
0
34
56
82
PM2.5
2007
295
196
99
0
0
0
0
41
60
82
PM2.5
2006
307
216
91
0
0
0
0
38
58
81
PM2.5
2005
326
256
68
2
0
0
0
36
57
114
PM2.5
2004
266
212
54
0
0
0
0
36
56
90
PM2.5
2003
42
34
8
0
0
0
0
30
55
65
PM2.5
2002
125
95
30
0
0
0
0
32
58
93
PM2.5
2001
129
106
23
0
0
0
0
32
56
85
PM2.5
2000
76
61
15
0
0
0
0
31
61
81
PM2.5
1999
71
70
0
1
0
0
0
21
37
102
PM10
1998
58
57
1
0
0
0
0
17
31
76
PM10
1997
60
60
0
0
0
0
0
23
36
42
PM10
1996
58
56
2
0
0
0
0
19
41
57
PM10
1995
61
59
2
0
0
0
0
20
31
81
PM10
1992
6
6
0
0
0
0
0
19
33
33
PM10
1991
45
42
3
0
0
0
0
19
42
72
PM10
1990
54
48
6
0
0
0
0
22
51
68
PM10
1989
49
46
3
0
0
0
0
20
40
85
PM10
1988
47
45
2
0
0
0
0
19
45
62
PM10
1987
47
43
3
1
0
0
0
22
44
102
PM10
1986
52
49
3
0
0
0
0
19
42
64
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 Idaho with a similar median AQI in 2025
