Daily Air Quality Index summaries from EPA monitors in Randolph, Illinois, 1989–2025.
68%
Good days in 2025
43
Median daily AQI, 2025
1
Days above 100 in 2025
364
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Randolph, Illinois on 364 days. 248 of those days (68%) were in the Good range, and the median daily AQI was 43. That median is about the same as the typical monitored county in Illinois (median 42 across 23 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 223 days. Across the years with fuller monitoring, the share of Good days fell: an average of 74% in 1989–1991 versus 69% 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
Fine particles (PM2.5)
223
61%
Ozone
141
39%
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
364
248
115
0
1
0
0
43
61
161
PM2.5
2024
366
289
77
0
0
0
0
40
54
100
PM2.5
2023
365
215
137
11
2
0
0
46
68
156
PM2.5
2022
365
244
119
2
0
0
0
45
61
108
PM2.5
2021
355
223
131
1
0
0
0
45
61
122
PM2.5
2020
366
243
121
2
0
0
0
44
59
103
PM2.5
2019
324
234
90
0
0
0
0
43
58
97
Ozone
2018
363
225
137
1
0
0
0
46
61
129
PM2.5
2017
343
153
189
1
0
0
0
52
67
115
PM2.5
2016
295
209
85
1
0
0
0
42
61
119
Ozone
2015
257
198
59
0
0
0
0
42
58
90
Ozone
2014
230
159
67
4
0
0
0
44
71
122
Ozone
2013
301
270
31
0
0
0
0
38
51
93
Ozone
2012
355
271
60
22
2
0
0
38
87
161
Ozone
2011
353
314
39
0
0
0
0
36
51
97
Ozone
2010
353
305
48
0
0
0
0
36
55
97
Ozone
2009
364
330
34
0
0
0
0
33
50
91
Ozone
2008
363
298
65
0
0
0
0
37
58
87
Ozone
2007
360
257
84
19
0
0
0
41
78
140
Ozone
2006
353
266
83
4
0
0
0
39
71
122
Ozone
2005
362
255
100
7
0
0
0
41
80
129
Ozone
2004
362
293
69
0
0
0
0
38
60
97
Ozone
2003
363
279
74
10
0
0
0
40
71
136
Ozone
2002
364
269
72
20
3
0
0
37
84
169
Ozone
2001
365
275
81
9
0
0
0
38
71
140
Ozone
2000
366
255
99
11
1
0
0
41
84
151
Ozone
1999
352
242
92
16
2
0
0
41
80
156
Ozone
1998
363
265
78
20
0
0
0
38
87
150
Ozone
1997
365
285
74
6
0
0
0
36
67
115
Ozone
1996
366
291
57
17
1
0
0
36
67
166
Ozone
1995
365
258
84
22
0
1
0
40
84
203
Ozone
1994
365
249
98
15
3
0
0
40
85
169
Ozone
1993
365
312
50
3
0
0
0
33
57
136
Ozone
1992
366
273
78
15
0
0
0
39
69
150
Ozone
1991
365
275
74
16
0
0
0
36
79
143
Ozone
1990
363
283
70
9
1
0
0
35
77
171
Ozone
1989
223
156
65
2
0
0
0
33
66
102
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 Illinois with a similar median AQI in 2025
