Daily Air Quality Index summaries from EPA monitors in Lemhi, Idaho, 1990–2025.
72%
Good days in 2025
29
Median daily AQI, 2025
2
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 Lemhi, Idaho on 365 days. 261 of those days (72%) were in the Good range, and the median daily AQI was 29. 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 fell: an average of 90% in 1995–1997 versus 66% in 2023–2025.
Years with fewer than 120 monitored days (1993, 1994, 2001, 2002, 2003, 2004…) 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
261
102
1
1
0
0
29
63
163
PM2.5
2024
366
207
143
12
4
0
0
37
78
198
PM2.5
2023
363
251
110
2
0
0
0
32
63
119
PM2.5
2022
365
199
136
18
10
2
0
44
92
212
PM2.5
2021
365
188
157
16
4
0
0
47
83
172
PM2.5
2020
365
194
160
8
3
0
0
46
80
168
PM2.5
2019
360
237
119
4
0
0
0
31
72
133
PM2.5
2018
360
225
132
3
0
0
0
38
74
121
PM2.5
2017
358
214
113
23
8
0
0
37
98
193
PM2.5
2016
364
182
153
26
3
0
0
51
97
160
PM2.5
2015
355
176
154
17
5
3
0
51
91
267
PM2.5
2014
348
171
160
16
1
0
0
52
83
157
PM2.5
2013
346
173
159
12
2
0
0
51
85
159
PM2.5
2012
362
164
152
16
14
16
0
54
110
289
PM2.5
2011
359
192
155
11
1
0
0
46
85
153
PM2.5
2010
343
199
130
13
1
0
0
43
83
154
PM2.5
2009
354
238
110
6
0
0
0
33
68
117
PM2.5
2008
350
272
78
0
0
0
0
31
58
86
PM2.5
2007
316
223
81
6
4
2
0
35
70
247
PM2.5
2006
293
198
91
2
2
0
0
39
64
182
PM2.5
2005
298
185
107
5
1
0
0
38
70
151
PM2.5
2004
61
44
15
2
0
0
0
29
74
113
PM2.5
2003
61
57
4
0
0
0
0
24
48
89
PM10
2002
60
54
6
0
0
0
0
21
52
60
PM10
2001
65
55
10
0
0
0
0
29
52
64
PM10
2000
131
92
21
13
5
0
0
30
113
177
PM10
1999
136
128
8
0
0
0
0
20
46
79
PM2.5
1998
122
94
28
0
0
0
0
22
57
85
PM10
1997
125
112
12
1
0
0
0
20
51
101
PM2.5
1996
131
115
16
0
0
0
0
19
52
83
PM2.5
1995
136
125
11
0
0
0
0
16
47
81
PM2.5
1994
112
99
13
0
0
0
0
16
56
78
PM2.5
1993
63
46
17
0
0
0
0
25
64
98
PM10
1992
54
38
16
0
0
0
0
37
62
91
PM10
1991
33
25
8
0
0
0
0
38
64
96
PM10
1990
9
4
5
0
0
0
0
54
92
92
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
