Daily Air Quality Index summaries from EPA monitors in Winnebago, Wisconsin, 1980–2003.
69%
Good days in 2003
45
Median daily AQI, 2003
13
Days above 100 in 2003
201
Days with an AQI in 2003 (of 365)
In 2003, EPA reported a daily Air Quality Index (AQI) for Winnebago, Wisconsin on 201 days. 139 of those days (69%) were in the Good range, and the median daily AQI was 45. That median is about the same as the typical monitored county in Wisconsin (median 44 across 29 counties), and about the same as the typical monitored U.S. county (44). The main pollutant was ozone on 184 days. Across the years with fuller monitoring, the share of Good days fell: an average of 80% in 1980–1982 versus 65% in 2001–2003.
EPA did not report an AQI for every day of 2003 here (201 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.
The most recent year with data for this county is 2003; EPA's files for 2004–2025 contain no row for it, which usually means its monitors stopped reporting.
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, 2003
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
184
92%
Fine particles (PM2.5)
17
8%
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
2003
201
139
49
13
0
0
0
45
80
143
Ozone
2002
242
143
88
10
1
0
0
44
84
159
Ozone
2001
242
160
70
8
4
0
0
44
84
161
Ozone
2000
242
175
64
3
0
0
0
41
71
147
Ozone
1999
236
136
80
16
4
0
0
45
97
169
Ozone
1998
181
130
45
5
1
0
0
45
80
156
Ozone
1997
179
143
29
6
1
0
0
39
67
154
Ozone
1996
180
142
27
11
0
0
0
40
80
143
Ozone
1995
184
143
30
8
3
0
0
38
87
156
Ozone
1994
214
189
22
3
0
0
0
37
54
143
Ozone
1993
359
343
14
2
0
0
0
23
43
108
Ozone
1992
344
310
27
6
1
0
0
26
50
151
Ozone
1991
184
137
36
9
2
0
0
41
90
159
Ozone
1990
181
150
29
2
0
0
0
40
67
147
Ozone
1989
288
176
76
25
7
4
0
44
108
255
Ozone
1988
256
140
53
37
21
5
0
48
151
273
Ozone
1987
175
122
40
12
1
0
0
42
93
172
Ozone
1986
182
134
33
15
0
0
0
40
97
150
Ozone
1985
182
129
37
11
5
0
0
43
93
185
Ozone
1984
155
127
23
4
1
0
0
41
77
172
Ozone
1983
197
136
35
18
8
0
0
42
112
169
Ozone
1982
166
127
31
7
1
0
0
40
77
174
Ozone
1981
163
136
20
4
3
0
0
36
71
182
Ozone
1980
193
152
27
12
1
1
0
31
84
206
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.
