Median AQI
43
Good
Virginia · County air quality · 2025
Loudoun County, Virginia
Median AQI 43 (Good). 75.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 43
- Median AQI
- 75.8%
- Good-air days
- 0
- Unhealthy days
- 42%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Loudoun County's air is good on balance, more polluted than the median US county, a median AQI of 43 with 75.8% of 273 monitored days in the Good band, driven mainly by Ozone.
- 43
- median AQI · Good
- 75.8%
- days rated Good
- Ozone
- main pollutant
- 42%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 120.
Data updated July 2026
- Good · 207 d · 75.8%
- Moderate · 65 d · 23.8%
- USG · 1 d · 0.4%
How did Loudoun County's air break down in 2025?
Across 273 monitored days, 207 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 120 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 43 (Good).
Insights: Loudoun County, Virginia. EPA monitors recorded a median Air Quality Index of 43 across 273 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 207 (76%) fell in the Good band (AQI 0–50), 65 (24%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 120 (USG). Residents averaged about 22.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (165 days), PM2.5 (107 days), NO2 (1 days). Across the 2020–2025 trend window, good days shifted by -132 and the median AQI moved +9 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 120, 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
75.8%
207 of 273 monitored days
0.8pp vs 75% target
Max AQI Recorded
120
USG
Health Grade
Good
90th-pct AQI 61
Loudoun County, Good days share 75.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Loudoun 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 273 monitored days across EPA AQI categories.
Good
207
76%
Moderate
65
24%
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 Loudoun County.
- Ozone · 165 days · 60.4%
- PM2.5 · 107 days · 39.2%
- NO₂ · 1 days · 0.4%
Health Impact Assessment
Good
Loudoun County's air quality is rated Good based on 75.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 75.8% of monitored days in 2025, with a median AQI of 43. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 165 of 273 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Loudoun County. Best year: 2020 (339 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 339 | 26 | 1 | 0 | 34 | 108 |
| 2021 | 308 | 55 | 1 | 0 | 37 | 122 |
| 2022 | 328 | 34 | 2 | 0 | 37 | 112 |
| 2023 | 306 | 54 | 2 | 2 | 39 | 167 |
| 2024 | 245 | 121 | 0 | 0 | 43 | 87 |
| 2025 | 207 | 65 | 1 | 0 | 43 | 120 |
How does Loudoun County compare?
How Loudoun County compares
Good-day share worse than US avg
Loudoun County 75.8%
Albemarle County, Virginia 77.9%
US average 76.5%
Median AQI worse than US avg
Loudoun County 43
Albemarle County, Virginia 41
US average 38
Unhealthy days / yr about average
Loudoun 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 Loudoun County.
Allegan County, Michigan
AQI 43 · 71.2% good
Allen County, Ohio
AQI 43 · 65.9% good
Ashtabula County, Ohio
AQI 43 · 81.2% good
Bell County, Kentucky
AQI 43 · 63.5% good
Boise County, Idaho
AQI 43 · 72.9% good
Brazos County, Texas
AQI 43 · 63.4% good
What Loudoun 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 43 means for exposure. Health guidance
- See how Loudoun County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Loudoun County with its Virginia neighbours before drawing a conclusion about the region. All of Virginia
Based on 273 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 Loudoun County, Virginia? ▼
Loudoun County has a median Air Quality Index (AQI) of 43, rated "Good." 75.8% of monitored days (207 out of 273) had good air quality in 2025.
What is the main pollutant in Loudoun County? ▼
The primary pollutant in Loudoun County is Ozone (O3), which was the main AQI driver on 165 days (60% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Loudoun County have? ▼
In 2025, Loudoun County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 120.
Is the air quality in Loudoun County getting better or worse? ▼
Air quality in Loudoun County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 339 good days. Worst year: 2025 with 207 good days.
What does AQI 43 mean for health? ▼
Loudoun County's median AQI of 43 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 Loudoun County compare to other counties in Virginia? ▼
Loudoun County has 75.8% 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 Loudoun County? ▼
The 90th percentile AQI for Loudoun County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 120 (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.