Bad Air Days in Prince William County, Virginia: under 1 a Year
under 1 bad air day a year
Fewer bad air days than most monitored US counties. Ranked 751 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (0% particle days).
Which months to watch
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and April and May and September. Averaged over 2016 to 2025.
What to buy, and what not to
- Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
- On the odd bad day, check AirNow and keep windows shut.
The worst days on file
In 2000 to 2009 this county averaged 15 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2016, with 3 bad days on 366 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-06-01 | 129 | Ozone |
| 2021-05-20 | 119 | Ozone |
| 2016-06-01 | 112 | Ozone |
| 2023-06-02 | 112 | Ozone |
| 2016-04-19 | 105 | Ozone |
An ordinary day in Prince William
Across 3,608 monitored days from 2016 to 2025, the air in Prince William County rated Good on 93% of them, more often than the 72% typical of monitored counties, and Moderate on 7%. The median day sat at AQI 34; one day in ten went above 48.
The pollutant setting the AQI on an ordinary day here:
- ozone85%3,074 days
- nitrogen dioxide15%534 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 349 | 16 | 0 | 0 | 35 | 87 |
| 2024 | 366 | 339 | 27 | 0 | 0 | 35 | 87 |
| 2023 | 365 | 329 | 33 | 3 | 0 | 37 | 129 |
| 2022 | 350 | 337 | 13 | 0 | 0 | 35 | 93 |
| 2021 | 359 | 333 | 25 | 1 | 0 | 35 | 119 |
| 2020 | 364 | 357 | 7 | 0 | 0 | 32 | 74 |
| 2019 | 364 | 347 | 17 | 0 | 0 | 36 | 100 |
| 2018 | 345 | 316 | 29 | 0 | 0 | 32 | 100 |
| 2017 | 364 | 333 | 31 | 0 | 0 | 34 | 97 |
| 2016 | 366 | 323 | 40 | 3 | 0 | 31 | 112 |
| 2015 | 364 | 330 | 34 | 0 | 0 | 30 | 93 |
| 2014 | 363 | 332 | 30 | 1 | 0 | 30 | 119 |
| 2013 | 365 | 341 | 24 | 0 | 0 | 29 | 100 |
| 2012 | 365 | 301 | 58 | 6 | 0 | 31 | 140 |
| 2011 | 361 | 312 | 45 | 4 | 0 | 29 | 129 |
| 2010 | 365 | 293 | 68 | 4 | 1 | 31 | 169 |
*2025 may be a partial year in EPA's file.
Elsewhere in Virginia
- Arlington County3/yr
- Fairfax County3/yr
- Henrico County1/yr
- Loudoun County1/yr
- Frederick County1/yr
- Bristol Citythin data
- Suffolk Cityunder 1/yr
- Alexandria Citythin data
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.