Daily Air Quality Index summaries from EPA monitors in St. Croix, Wisconsin, 1980–2010.
77%
Good days in 2010
42
Median daily AQI, 2010
2
Days above 100 in 2010
264
Days with an AQI in 2010 (of 365)
In 2010, EPA reported a daily Air Quality Index (AQI) for St. Croix, Wisconsin on 264 days. 202 of those days (77%) were in the Good range, and the median daily AQI was 42. That median is about the same as the typical monitored county in Wisconsin (median 40 across 31 counties), and about the same as the typical monitored U.S. county (44). The main pollutant was ozone on 187 days. Across the years with fuller monitoring, the share of Good days fell: an average of 82% in 1980–1982 versus 77% in 2008–2010.
EPA did not report an AQI for every day of 2010 here (264 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 2010; EPA's files for 2011–2025 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, 2010
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
187
71%
Fine particles (PM2.5)
77
29%
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
2010
264
202
60
2
0
0
0
42
58
124
Ozone
2009
314
246
67
1
0
0
0
38
61
130
Ozone
2008
365
281
82
2
0
0
0
38
61
128
Ozone
2007
362
273
83
6
0
0
0
37
63
129
Ozone
2006
360
268
89
3
0
0
0
39
61
119
Ozone
2005
296
213
78
3
2
0
0
39
66
155
Ozone
2004
225
189
36
0
0
0
0
37
59
93
Ozone
2003
184
132
45
7
0
0
0
44
77
136
Ozone
2002
209
151
54
4
0
0
0
42
67
140
Ozone
2001
204
161
38
4
1
0
0
41
64
159
Ozone
2000
209
155
47
7
0
0
0
40
76
122
Ozone
1999
204
147
49
8
0
0
0
41
77
133
Ozone
1998
167
130
30
7
0
0
0
41
64
136
Ozone
1997
171
146
20
5
0
0
0
38
64
140
Ozone
1996
177
169
6
2
0
0
0
36
46
112
Ozone
1995
172
154
15
3
0
0
0
35
51
147
Ozone
1994
287
268
16
3
0
0
0
27
48
126
Ozone
1993
365
359
6
0
0
0
0
23
39
87
CO
1992
366
347
15
4
0
0
0
18
43
129
CO
1991
234
204
29
1
0
0
0
30
58
108
Ozone
1990
184
156
27
1
0
0
0
40
61
122
Ozone
1989
176
134
38
4
0
0
0
41
74
147
Ozone
1988
164
100
43
15
5
1
0
44
105
218
Ozone
1987
180
133
37
9
1
0
0
42
84
166
Ozone
1986
176
154
19
3
0
0
0
38
54
150
Ozone
1985
170
134
30
5
1
0
0
41
77
151
Ozone
1984
175
144
28
3
0
0
0
38
61
143
Ozone
1983
123
100
18
5
0
0
0
40
67
126
Ozone
1982
170
134
32
4
0
0
0
40
74
140
Ozone
1981
138
112
24
2
0
0
0
39
67
150
Ozone
1980
163
141
17
2
3
0
0
29
61
161
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.
Counties in Wisconsin with a similar median AQI in 2010
