Daily Air Quality Index summaries from EPA monitors in Jersey, Illinois, 1988–2025.
72%
Good days in 2025
42
Median daily AQI, 2025
4
Days above 100 in 2025
358
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Jersey, Illinois on 358 days. 259 of those days (72%) were in the Good range, and the median daily AQI was 42. That median is about the same as the typical monitored county in Illinois (median 42 across 23 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 190 days. Across the years with fuller monitoring, the share of Good days rose: an average of 61% in 1988–1990 versus 67% in 2023–2025.
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
Ozone
190
53%
Fine particles (PM2.5)
168
47%
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
358
259
95
3
1
0
0
42
67
156
Ozone
2024
333
248
84
1
0
0
0
42
61
112
Ozone
2023
365
199
148
17
1
0
0
48
77
166
PM2.5
2022
365
240
120
5
0
0
0
45
61
112
PM2.5
2021
360
225
133
2
0
0
0
45
61
112
PM2.5
2020
358
258
99
1
0
0
0
44
58
112
PM2.5
2019
347
221
124
2
0
0
0
46
62
119
PM2.5
2018
356
208
145
3
0
0
0
47
66
122
PM2.5
2017
309
170
136
3
0
0
0
48
64
119
PM2.5
2016
295
202
88
5
0
0
0
44
65
150
Ozone
2015
240
190
49
1
0
0
0
41
60
112
Ozone
2014
233
178
54
1
0
0
0
40
64
101
Ozone
2013
211
168
41
1
1
0
0
41
61
151
Ozone
2012
212
120
65
22
4
1
0
49
108
202
Ozone
2011
213
156
47
9
1
0
0
44
80
156
Ozone
2010
262
197
61
4
0
0
0
38
67
108
Ozone
2009
243
189
52
2
0
0
0
40
61
115
Ozone
2008
244
180
61
2
1
0
0
42
64
159
Ozone
2007
243
161
71
11
0
0
0
44
87
150
Ozone
2006
264
188
70
6
0
0
0
42
67
143
Ozone
2005
227
121
84
18
4
0
0
48
100
159
Ozone
2004
237
153
76
8
0
0
0
44
77
122
Ozone
2003
214
136
57
19
2
0
0
47
100
174
Ozone
2002
207
129
47
22
7
2
0
45
122
205
Ozone
2001
213
125
68
17
3
0
0
47
100
172
Ozone
2000
230
163
47
19
1
0
0
43
100
154
Ozone
1999
238
152
54
21
11
0
0
44
115
197
Ozone
1998
233
148
61
18
6
0
0
46
101
190
Ozone
1997
227
151
53
21
2
0
0
46
105
182
Ozone
1996
229
177
40
10
2
0
0
42
74
177
Ozone
1995
228
168
39
16
5
0
0
43
93
174
Ozone
1994
222
158
51
10
3
0
0
42
87
161
Ozone
1993
223
187
27
8
1
0
0
38
61
164
Ozone
1992
195
139
43
11
2
0
0
42
84
182
Ozone
1991
220
146
52
15
7
0
0
44
101
190
Ozone
1990
217
151
47
14
5
0
0
43
100
200
Ozone
1989
235
158
60
13
4
0
0
44
90
195
Ozone
1988
208
97
55
28
22
6
0
58
159
232
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 Illinois with a similar median AQI in 2025
