Daily Air Quality Index summaries from EPA monitors in Sauk, Wisconsin, 1985–2025.
76%
Good days in 2025
35
Median daily AQI, 2025
6
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 Sauk, Wisconsin on 365 days. 276 of those days (76%) were in the Good range, and the median daily AQI was 35. That median is lower than the typical monitored county in Wisconsin (median 38 across 29 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 237 days. Across the years with fuller monitoring, the share of Good days fell: an average of 84% in 1995–1997 versus 74% in 2023–2025.
Years with fewer than 120 monitored days (1985, 1986) 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)
237
65%
Ozone
127
35%
Coarse particles (PM10)
1
<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
276
83
5
1
0
0
35
58
167
PM2.5
2024
366
312
54
0
0
0
0
37
53
77
PM2.5
2023
362
218
123
16
4
1
0
44
77
271
PM2.5
2022
360
265
95
0
0
0
0
41
58
79
PM2.5
2021
365
236
129
0
0
0
0
44
65
96
PM2.5
2020
366
264
101
1
0
0
0
41
59
112
PM2.5
2019
365
281
83
1
0
0
0
39
59
107
PM2.5
2018
365
265
99
1
0
0
0
42
63
122
Ozone
2017
364
270
94
0
0
0
0
39
58
87
PM2.5
2016
366
300
65
1
0
0
0
35
56
101
PM2.5
2015
364
273
91
0
0
0
0
40
58
96
PM2.5
2014
365
258
104
3
0
0
0
40
59
115
PM2.5
2013
364
245
119
0
0
0
0
42
62
90
PM2.5
2012
365
223
136
5
1
0
0
44
74
151
PM2.5
2011
284
230
54
0
0
0
0
40
58
92
Ozone
2010
270
213
56
1
0
0
0
40
58
111
Ozone
2009
313
249
61
3
0
0
0
36
63
115
Ozone
2008
361
281
78
2
0
0
0
39
62
115
Ozone
2007
365
263
98
4
0
0
0
39
68
140
Ozone
2006
349
268
79
2
0
0
0
39
64
114
Ozone
2005
365
256
98
11
0
0
0
42
77
147
Ozone
2004
345
273
71
1
0
0
0
38
59
113
Ozone
2003
357
268
77
12
0
0
0
37
70
126
Ozone
2002
260
208
42
10
0
0
0
37
74
133
Ozone
2001
183
137
38
8
0
0
0
43
71
122
Ozone
2000
179
135
37
7
0
0
0
42
71
147
Ozone
1999
287
224
47
14
2
0
0
41
80
185
Ozone
1998
365
298
56
10
1
0
0
38
67
154
Ozone
1997
363
307
51
5
0
0
0
36
67
143
Ozone
1996
366
314
45
7
0
0
0
36
58
133
Ozone
1995
234
192
34
5
3
0
0
34
80
185
Ozone
1986
85
84
1
0
0
0
0
19
35
57
PM10
1985
66
65
1
0
0
0
0
21
35
53
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 Wisconsin with a similar median AQI in 2025
