Prince William County, Virginia air quality history
Daily Air Quality Index summaries from EPA monitors in Prince William, Virginia, 1980–2025.
96%
Good days in 2025
35
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 Prince William, Virginia on 365 days. 349 of those days (96%) were in the Good range, and the median daily AQI was 35. That median is about the same as the typical monitored county in Virginia (median 37 across 25 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 360 days. Across the years with fuller monitoring, the share of Good days rose: an average of 63% in 1991–1993 versus 93% in 2023–2025.
Years with fewer than 120 monitored days (1980, 1990) 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
Ozone
360
99%
Nitrogen dioxide (NO₂)
5
1%
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
349
16
0
0
0
0
35
46
87
Ozone
2024
366
339
27
0
0
0
0
35
49
87
Ozone
2023
365
329
33
3
0
0
0
37
50
129
Ozone
2022
350
337
13
0
0
0
0
35
46
93
Ozone
2021
359
333
25
1
0
0
0
35
49
119
Ozone
2020
364
357
7
0
0
0
0
32
44
74
Ozone
2019
364
347
17
0
0
0
0
36
48
100
Ozone
2018
345
316
29
0
0
0
0
32
48
100
Ozone
2017
364
333
31
0
0
0
0
34
49
97
Ozone
2016
366
323
40
3
0
0
0
31
51
112
Ozone
2015
364
330
34
0
0
0
0
30
50
93
Ozone
2014
363
332
30
1
0
0
0
30
49
119
Ozone
2013
365
341
24
0
0
0
0
29
48
100
Ozone
2012
365
301
58
6
0
0
0
31
67
140
Ozone
2011
361
312
45
4
0
0
0
29
61
129
Ozone
2010
365
293
68
3
1
0
0
31
67
169
Ozone
2009
363
331
32
0
0
0
0
27
49
93
Ozone
2008
366
311
48
7
0
0
0
31
64
140
Ozone
2007
338
251
70
17
0
0
0
37
87
140
Ozone
2006
365
294
58
9
4
0
0
31
74
182
Ozone
2005
364
299
53
12
0
0
0
31
71
112
Ozone
2004
362
311
43
7
1
0
0
32
61
179
Ozone
2003
365
310
46
5
3
1
0
33
64
204
Ozone
2002
360
271
49
34
5
1
0
34
108
203
Ozone
2001
365
283
58
18
6
0
0
34
90
187
Ozone
2000
366
306
45
13
2
0
0
32
71
169
Ozone
1999
358
253
57
40
8
0
0
37
108
177
Ozone
1998
342
239
62
30
9
2
0
35
108
208
Ozone
1997
364
280
56
24
4
0
0
34
93
187
Ozone
1996
357
278
56
21
2
0
0
34
80
159
Ozone
1995
365
267
67
22
8
1
0
33
97
208
Ozone
1994
283
216
58
9
0
0
0
39
77
150
Ozone
1993
235
128
63
36
8
0
0
48
122
179
Ozone
1992
195
143
39
11
2
0
0
38
93
179
Ozone
1991
237
142
58
28
9
0
0
45
119
179
Ozone
1990
10
10
0
0
0
0
0
20
41
41
PM10
1980
86
18
39
20
9
0
0
90
154
185
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
