Daily Air Quality Index summaries from EPA monitors in Nez Perce, Idaho, 1986–2025.
72%
Good days in 2025
33
Median daily AQI, 2025
4
Days above 100 in 2025
363
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Nez Perce, Idaho on 363 days. 263 of those days (72%) were in the Good range, and the median daily AQI was 33. That median is about the same as 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 363 days. Across the years with fuller monitoring, the share of Good days fell: an average of 96% in 1995–1997 versus 73% in 2023–2025.
Years with fewer than 120 monitored days (1991, 1992, 1993, 1994, 2003, 2013…) 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)
363
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
363
263
96
3
1
0
0
33
63
161
PM2.5
2024
366
276
82
7
1
0
0
29
62
182
PM2.5
2023
365
256
106
2
1
0
0
36
61
199
PM2.5
2022
365
252
107
2
4
0
0
34
63
195
PM2.5
2021
365
251
96
15
2
1
0
34
77
204
PM2.5
2020
366
279
76
4
0
6
1
28
63
475
PM2.5
2019
360
272
88
0
0
0
0
32
61
90
PM2.5
2018
365
273
87
4
1
0
0
25
67
188
PM2.5
2017
365
252
98
6
6
3
0
36
71
286
PM2.5
2016
366
287
77
2
0
0
0
31
57
141
PM2.5
2015
271
216
41
7
5
1
1
25
59
354
PM2.5
2013
61
58
3
0
0
0
0
23
43
63
PM2.5
2012
365
298
61
1
5
0
0
24
55
196
PM2.5
2011
365
329
36
0
0
0
0
22
50
72
PM2.5
2010
357
322
35
0
0
0
0
22
50
72
PM2.5
2009
332
304
28
0
0
0
0
23
48
73
PM2.5
2008
327
287
40
0
0
0
0
24
52
78
PM2.5
2007
357
309
48
0
0
0
0
25
54
78
PM2.5
2006
334
251
77
6
0
0
0
30
59
121
PM2.5
2005
331
295
36
0
0
0
0
27
51
71
PM2.5
2004
295
234
61
0
0
0
0
33
55
70
PM2.5
2003
59
42
17
0
0
0
0
32
61
69
PM2.5
2002
202
169
33
0
0
0
0
22
58
97
PM2.5
2001
363
318
45
0
0
0
0
18
53
95
CO
2000
366
334
32
0
0
0
0
17
46
95
CO
1999
365
351
12
2
0
0
0
16
38
111
CO
1998
362
355
7
0
0
0
0
18
36
71
CO
1997
348
338
10
0
0
0
0
17
35
72
CO
1996
360
353
7
0
0
0
0
18
39
71
CO
1995
348
327
21
0
0
0
0
20
43
85
CO
1994
70
58
12
0
0
0
0
28
55
67
PM10
1993
61
46
15
0
0
0
0
34
63
76
PM10
1992
61
57
4
0
0
0
0
29
46
58
PM10
1991
56
44
11
0
1
0
0
32
65
191
PM10
1990
51
46
5
0
0
0
0
26
50
93
PM10
1989
62
50
12
0
0
0
0
33
60
80
PM10
1988
49
39
10
0
0
0
0
28
58
89
PM10
1987
29
22
7
0
0
0
0
34
61
76
PM10
1986
54
46
8
0
0
0
0
32
56
70
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
