Median AQI
44
Good
Virginia · County air quality · 2025
Fairfax County, Virginia
Median AQI 44 (Good). 74.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 74.8%
- Good-air days
- 0
- Unhealthy days
- 41%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Fairfax County's air is good on balance, more polluted than the median US county, a median AQI of 44 with 74.8% of 274 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 74.8%
- days rated Good
- Ozone
- main pollutant
- 41%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 124.
Data updated July 2026
- Good · 205 d · 74.8%
- Moderate · 68 d · 24.8%
- USG · 1 d · 0.4%
How did Fairfax County's air break down in 2025?
Across 274 monitored days, 205 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 124 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 274 days monitored. Median AQI: 44 (Good).
Insights: Fairfax County, Virginia. EPA monitors recorded a median Air Quality Index of 44 across 274 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 205 (75%) fell in the Good band (AQI 0–50), 68 (25%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 64, while the worst single-day peak hit 124 (USG). Residents averaged about 22.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (145 days), PM2.5 (113 days), NO2 (15 days), CO (1 days). Across the 2020–2025 trend window, good days shifted by -31 and the median AQI moved +0 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 124, usg 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
74.8%
205 of 274 monitored days
-0.2pp vs 75% target
Max AQI Recorded
124
USG
Health Grade
Moderate
90th-pct AQI 64
Fairfax County, Good days share 74.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Fairfax 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 274 monitored days across EPA AQI categories.
Good
205
75%
Moderate
68
25%
USG
1
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 Fairfax County.
- Ozone · 145 days · 52.9%
- PM2.5 · 113 days · 41.2%
- NO₂ · 15 days · 5.5%
- CO · 1 days · 0.4%
Health Impact Assessment
Moderate
Fairfax County's air quality is rated Moderate based on 74.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 74.8% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 145 of 274 monitored days.
5-Year Air Quality Trend
Air quality is improving in Fairfax County. Best year: 2024 (263 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 236 | 130 | 0 | 0 | 44 | 100 |
| 2021 | 208 | 153 | 4 | 0 | 47 | 129 |
| 2022 | 232 | 133 | 0 | 0 | 47 | 87 |
| 2023 | 217 | 138 | 7 | 2 | 46 | 222 |
| 2024 | 263 | 100 | 3 | 0 | 42 | 112 |
| 2025 | 205 | 68 | 1 | 0 | 44 | 124 |
How does Fairfax County compare?
How Fairfax County compares
Good-day share worse than US avg
Fairfax County 74.8%
Albemarle County, Virginia 77.9%
US average 76.5%
Median AQI worse than US avg
Fairfax County 44
Albemarle County, Virginia 41
US average 38
Unhealthy days / yr about average
Fairfax 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 Fairfax County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Fairfax 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 44 means for exposure. Health guidance
- See how Fairfax County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Fairfax County with its Virginia neighbours before drawing a conclusion about the region. All of Virginia
Based on 274 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 Fairfax County, Virginia? ▼
Fairfax County has a median Air Quality Index (AQI) of 44, rated "Good." 74.8% of monitored days (205 out of 274) had good air quality in 2025.
What is the main pollutant in Fairfax County? ▼
The primary pollutant in Fairfax County is Ozone (O3), which was the main AQI driver on 145 days (53% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Fairfax County have? ▼
In 2025, Fairfax County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 124.
Is the air quality in Fairfax County getting better or worse? ▼
Air quality in Fairfax County is improving based on 5-year trends (2020-2025). Best year: 2024 with 263 good days. Worst year: 2025 with 205 good days.
What does AQI 44 mean for health? ▼
Fairfax County's median AQI of 44 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 Fairfax County compare to other counties in Virginia? ▼
Fairfax County has 74.8% 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 Fairfax County? ▼
The 90th percentile AQI for Fairfax County is 64, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 124 (USG).
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.