Daily Air Quality Index summaries from EPA monitors in Johnson, Iowa, 1980–2025.
70%
Good days in 2025
37
Median daily AQI, 2025
4
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 Johnson, Iowa on 365 days. 256 of those days (70%) were in the Good range, and the median daily AQI was 37. That median is lower than the typical monitored county in Iowa (median 43.5 across 14 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 365 days. Across the years with fuller monitoring, the share of Good days fell: an average of 79% in 1981–1983 versus 60% in 2023–2025.
Years with fewer than 120 monitored days (1980, 1985, 1999) 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)
365
100%
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
256
105
3
1
0
0
37
61
159
PM2.5
2024
366
259
107
0
0
0
0
39
57
83
PM2.5
2023
365
143
216
2
3
1
0
53
68
210
PM2.5
2022
365
223
141
1
0
0
0
44
62
108
PM2.5
2021
364
172
190
2
0
0
0
52
67
121
PM2.5
2020
362
207
154
1
0
0
0
47
63
105
PM2.5
2019
364
210
154
0
0
0
0
46
64
92
PM2.5
2018
362
186
176
0
0
0
0
50
61
93
PM2.5
2017
364
216
148
0
0
0
0
44
61
82
PM2.5
2016
366
236
130
0
0
0
0
44
58
100
PM2.5
2015
365
198
166
1
0
0
0
48
64
139
PM2.5
2014
364
201
162
1
0
0
0
47
65
108
PM2.5
2013
365
160
204
1
0
0
0
53
67
103
PM2.5
2012
366
119
247
0
0
0
0
55
69
91
PM2.5
2011
364
94
270
0
0
0
0
56
74
97
PM2.5
2010
365
84
277
4
0
0
0
57
78
112
PM2.5
2009
356
136
218
2
0
0
0
53
72
109
PM2.5
2008
348
174
172
2
0
0
0
51
69
120
PM2.5
2007
332
148
179
5
0
0
0
53
72
149
PM2.5
2006
120
56
63
1
0
0
0
52
71
104
PM2.5
2005
122
43
74
5
0
0
0
55
77
131
PM2.5
2004
122
60
59
3
0
0
0
51
71
108
PM2.5
2003
121
54
66
1
0
0
0
52
72
109
PM2.5
2002
121
56
65
0
0
0
0
52
71
88
PM2.5
2001
121
54
65
2
0
0
0
52
73
136
PM2.5
2000
122
63
59
0
0
0
0
50
74
97
PM2.5
1999
116
45
69
2
0
0
0
55
74
104
PM2.5
1991
126
123
3
0
0
0
0
30
42
90
Ozone
1990
323
277
40
5
1
0
0
32
61
154
Ozone
1989
270
223
41
6
0
0
0
35
71
140
Ozone
1988
361
285
52
20
4
0
0
32
84
156
Ozone
1987
354
296
52
6
0
0
0
31
67
133
Ozone
1986
304
280
23
1
0
0
0
32
49
101
Ozone
1985
119
112
6
1
0
0
0
33
48
112
Ozone
1984
345
272
42
25
5
1
0
33
87
206
Ozone
1983
305
226
40
21
14
4
0
35
119
219
Ozone
1982
303
256
42
5
0
0
0
34
61
140
Ozone
1981
158
126
22
8
2
0
0
6
80
169
Ozone
1980
106
100
6
0
0
0
0
14
43
97
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 Iowa with a similar median AQI in 2025
