Daily Air Quality Index summaries from EPA monitors in Hardin, Kentucky, 1980–2025.
73%
Good days in 2025
43
Median daily AQI, 2025
0
Days above 100 in 2025
304
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Hardin, Kentucky on 304 days. 223 of those days (73%) were in the Good range, and the median daily AQI was 43. That median is higher than the typical monitored county in Kentucky (median 39 across 25 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 165 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 71% in 1980–1982 versus 73% 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
165
54%
Fine particles (PM2.5)
139
46%
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
304
223
81
0
0
0
0
43
58
97
Ozone
2024
154
129
25
0
0
0
0
41
53
67
PM2.5
2023
365
225
136
3
1
0
0
45
66
151
PM2.5
2022
362
242
120
0
0
0
0
44
58
86
PM2.5
2021
364
238
125
1
0
0
0
43
62
101
PM2.5
2020
366
268
98
0
0
0
0
43
56
80
PM2.5
2019
363
261
102
0
0
0
0
44
57
72
PM2.5
2018
361
191
170
0
0
0
0
49
64
100
PM2.5
2017
365
178
187
0
0
0
0
51
62
87
PM2.5
2016
364
152
211
1
0
0
0
52
66
101
PM2.5
2015
365
175
189
1
0
0
0
51
66
105
PM2.5
2014
341
172
169
0
0
0
0
50
65
88
PM2.5
2013
364
154
210
0
0
0
0
53
66
90
PM2.5
2012
307
171
129
5
2
0
0
47
75
161
PM2.5
2011
339
197
141
1
0
0
0
47
74
112
PM2.5
2010
343
143
195
5
0
0
0
53
71
115
PM2.5
2009
360
201
158
1
0
0
0
48
65
101
PM2.5
2008
360
174
182
4
0
0
0
51
74
122
PM2.5
2007
324
165
137
21
1
0
0
50
97
161
Ozone
2006
287
150
125
12
0
0
0
50
84
136
Ozone
2005
285
130
129
26
0
0
0
53
97
143
Ozone
2004
285
175
107
3
0
0
0
46
71
143
Ozone
2003
282
147
126
9
0
0
0
49
84
143
Ozone
2002
280
138
117
23
2
0
0
51
97
185
Ozone
2001
282
128
130
21
3
0
0
53
97
161
Ozone
2000
262
133
116
9
4
0
0
50
92
179
Ozone
1999
210
71
97
34
8
0
0
61
133
192
Ozone
1998
238
164
54
19
1
0
0
44
93
164
Ozone
1997
235
197
33
5
0
0
0
36
71
112
Ozone
1996
235
155
63
16
1
0
0
44
90
166
Ozone
1995
234
123
76
27
7
1
0
48
108
206
Ozone
1994
230
146
50
23
11
0
0
44
119
192
Ozone
1993
204
146
43
11
3
1
0
44
93
212
Ozone
1992
138
114
23
1
0
0
0
39
58
101
Ozone
1983
177
91
50
28
8
0
0
50
119
192
Ozone
1982
191
138
49
4
0
0
0
41
77
119
Ozone
1981
192
139
47
6
0
0
0
44
71
122
Ozone
1980
208
145
43
17
3
0
0
42
100
174
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 Kentucky with a similar median AQI in 2025
