Median AQI
38
Good
Virginia · County air quality · 2025
Prince William County, Virginia
Median AQI 38 (Good). 94.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 94.1%
- Good-air days
- 0
- Unhealthy days
- 86%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Prince William County's air is good on balance, cleaner than most US counties, a median AQI of 38 with 94.1% of 272 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 94.1%
- days rated Good
- Ozone
- main pollutant
- 86%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 87.
Data updated July 2026
- Good · 256 d · 94.1%
- Moderate · 16 d · 5.9%
How did Prince William County's air break down in 2025?
Across 272 monitored days, 256 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 87 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 272 days monitored. Median AQI: 38 (Good).
Insights: Prince William County, Virginia. EPA monitors recorded a median Air Quality Index of 38 across 272 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 256 (94%) fell in the Good band (AQI 0–50), 16 (6%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 48, while the worst single-day peak hit 87 (Moderate). Residents averaged about 28.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (270 days), NO2 (2 days). Across the 2020–2025 trend window, good days shifted by -101 and the median AQI moved +6 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 87, moderate but never Unhealthy. Nearby counties show comparable readings: Albemarle (77.9% good, AQI 41); Arlington (84.8% good, AQI 40); Bristol City (78.3% good, AQI 33); Caroline (96.2% good, AQI 37); Carroll (100.0% good, AQI 9); Charles (88.6% good, AQI 38).
Air Quality Summary
Good Days
94.1%
256 of 272 monitored days
19.1pp vs 75% target
Max AQI Recorded
87
Moderate
Health Grade
Excellent
90th-pct AQI 48
Prince William County, Good days share 94.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Prince William County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 272 monitored days across EPA AQI categories.
Good
256
94%
Moderate
16
6%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Prince William County.
- Ozone · 270 days · 99.3%
- NO₂ · 2 days · 0.7%
Health Impact Assessment
Excellent
Prince William County's air quality is rated Excellent based on 94.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 94.1% of monitored days in 2025, with a median AQI of 38. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 270 of 272 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Prince William County. Best year: 2020 (357 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 357 | 7 | 0 | 0 | 32 | 74 |
| 2021 | 333 | 25 | 1 | 0 | 35 | 119 |
| 2022 | 337 | 13 | 0 | 0 | 35 | 93 |
| 2023 | 329 | 33 | 3 | 0 | 37 | 129 |
| 2024 | 339 | 27 | 0 | 0 | 35 | 87 |
| 2025 | 256 | 16 | 0 | 0 | 38 | 87 |
How does Prince William County compare?
How Prince William County compares
Good-day share better than US avg
Prince William County 94.1%
Albemarle County, Virginia 77.9%
US average 76.5%
Median AQI about average
Prince William County 38
Albemarle County, Virginia 41
US average 38
Unhealthy days / yr about average
Prince William County 0
Albemarle County, Virginia 0
US average 0
Other Counties in Virginia
Air quality comparison for nearby counties in Virginia.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Prince William County.
Adams County, Illinois
AQI 38 · 94.4% good
Anoka County, Minnesota
AQI 38 · 82.1% good
Atlantic County, New Jersey
AQI 38 · 79.6% good
Avery County, North Carolina
AQI 38 · 93.9% good
Barnstable County, Massachusetts
AQI 38 · 92.5% good
Bay County, Michigan
AQI 38 · 71.8% good
What Prince William County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 38 means for exposure. Health guidance
- See how Prince William County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Prince William County with its Virginia neighbours before drawing a conclusion about the region. All of Virginia
Based on 272 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Prince William County, Virginia? ▼
Prince William County has a median Air Quality Index (AQI) of 38, rated "Good." 94.1% of monitored days (256 out of 272) had good air quality in 2025.
What is the main pollutant in Prince William County? ▼
The primary pollutant in Prince William County is Ozone (O3), which was the main AQI driver on 270 days (99% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Prince William County have? ▼
In 2025, Prince William County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
Is the air quality in Prince William County getting better or worse? ▼
Air quality in Prince William County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 357 good days. Worst year: 2025 with 256 good days.
What does AQI 38 mean for health? ▼
Prince William County's median AQI of 38 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Prince William County compare to other counties in Virginia? ▼
Prince William County has 94.1% good air days. Nearby counties in Virginia: Albemarle (77.9% good), Arlington (84.8% good), Bristol City (78.3% good), Caroline (96.2% good), Carroll (100.0% good), Charles (88.6% good).
What is the 90th percentile AQI in Prince William County? ▼
The 90th percentile AQI for Prince William County is 48, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (Moderate).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.