Daily Air Quality Index summaries from EPA monitors in Frederick, Virginia, 1992–2025.
74%
Good days in 2025
39
Median daily AQI, 2025
0
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 Frederick, Virginia on 365 days. 270 of those days (74%) were in the Good range, and the median daily AQI was 39. That median is about the same as the typical monitored county in Virginia (median 37 across 25 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 227 days. Across the years with fuller monitoring, the share of Good days rose: an average of 63% in 1992–1994 versus 71% 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)
227
62%
Ozone
138
38%
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
270
95
0
0
0
0
39
58
85
PM2.5
2024
355
264
90
1
0
0
0
41
57
102
PM2.5
2023
363
240
114
5
4
0
0
44
66
185
PM2.5
2022
334
234
100
0
0
0
0
43
58
89
PM2.5
2021
362
222
140
0
0
0
0
44
61
98
PM2.5
2020
304
249
55
0
0
0
0
39
53
81
PM2.5
2019
365
277
88
0
0
0
0
42
55
96
PM2.5
2018
352
267
85
0
0
0
0
40
58
87
PM2.5
2017
344
253
91
0
0
0
0
42
56
80
PM2.5
2016
358
256
102
0
0
0
0
42
60
90
PM2.5
2015
342
213
129
0
0
0
0
45
64
86
PM2.5
2014
362
222
140
0
0
0
0
45
62
93
PM2.5
2013
365
229
135
1
0
0
0
45
62
115
PM2.5
2012
361
180
178
3
0
0
0
51
69
119
PM2.5
2011
365
183
181
1
0
0
0
50
69
101
PM2.5
2010
261
155
102
3
1
0
0
46
71
159
Ozone
2009
261
179
81
1
0
0
0
43
64
101
Ozone
2008
265
165
94
6
0
0
0
44
71
136
Ozone
2007
246
159
80
7
0
0
0
45
80
140
Ozone
2006
240
180
52
7
1
0
0
43
77
156
Ozone
2005
232
153
64
15
0
0
0
44
87
136
Ozone
2004
214
167
45
1
1
0
0
41
74
159
Ozone
2003
214
153
53
7
1
0
0
42
80
172
Ozone
2002
214
127
54
25
8
0
0
47
115
179
Ozone
2001
208
124
65
14
5
0
0
47
100
156
Ozone
2000
214
159
45
8
2
0
0
39
84
156
Ozone
1999
213
113
64
33
3
0
0
50
112
169
Ozone
1998
214
106
59
40
8
1
0
51
126
201
Ozone
1997
207
119
58
26
4
0
0
48
112
172
Ozone
1996
213
136
62
15
0
0
0
44
93
150
Ozone
1995
213
126
61
23
3
0
0
47
108
166
Ozone
1994
214
131
63
18
2
0
0
46
100
169
Ozone
1993
211
128
66
16
1
0
0
46
93
164
Ozone
1992
214
143
56
14
1
0
0
44
90
159
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 Virginia with a similar median AQI in 2025
