Median AQI
40
Good
Vermont · County air quality · 2025
Chittenden County, Vermont
Median AQI 40 (Good). 91.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 40
- Median AQI
- 91.2%
- Good-air days
- 0
- Unhealthy days
- 79%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Chittenden County's air is good on balance, cleaner than most US counties, a median AQI of 40 with 91.2% of 182 monitored days in the Good band, driven mainly by Ozone.
- 40
- median AQI · Good
- 91.2%
- days rated Good
- Ozone
- main pollutant
- 79%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 108.
Data updated July 2026
- Good · 166 d · 91.2%
- Moderate · 14 d · 7.7%
- USG · 2 d · 1.1%
How did Chittenden County's air break down in 2025?
Across 182 monitored days, 166 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 182 days monitored. Median AQI: 40 (Good).
Insights: Chittenden County, Vermont. EPA monitors recorded a median Air Quality Index of 40 across 182 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 166 (91%) fell in the Good band (AQI 0–50), 14 (8%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 108 (USG). Residents averaged about 27.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (161 days), PM2.5 (20 days), CO (1 days). Across the 2020–2025 trend window, good days shifted by -136 and the median AQI moved +1 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 108, usg but never Unhealthy. Nearby counties show comparable readings: Bennington (82.9% good, AQI 39); Rutland (78.9% good, AQI 38); Windham (100.0% good, AQI 12).
Air Quality Summary
Good Days
91.2%
166 of 182 monitored days
16.2pp vs 75% target
Max AQI Recorded
108
USG
Health Grade
Excellent
90th-pct AQI 49
Chittenden County, Good days share 91.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Chittenden 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 182 monitored days across EPA AQI categories.
Good
166
91%
Moderate
14
8%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Chittenden County.
- Ozone · 161 days · 88.5%
- PM2.5 · 20 days · 11.0%
- CO · 1 days · 0.5%
Health Impact Assessment
Excellent
Chittenden County's air quality is rated Excellent based on 91.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 91.2% of monitored days in 2025, with a median AQI of 40. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 161 of 182 monitored days.
5-Year Air Quality Trend
Air quality is improving in Chittenden County. Best year: 2024 (323 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 302 | 64 | 0 | 0 | 39 | 98 |
| 2021 | 288 | 76 | 1 | 0 | 40 | 129 |
| 2022 | 298 | 67 | 0 | 0 | 41 | 90 |
| 2023 | 259 | 100 | 4 | 2 | 42 | 160 |
| 2024 | 323 | 43 | 0 | 0 | 37 | 84 |
| 2025 | 166 | 14 | 2 | 0 | 40 | 108 |
How does Chittenden County compare?
How Chittenden County compares
Good-day share better than US avg
Chittenden County 91.2%
Bennington County, Vermont 82.9%
US average 76.5%
Median AQI worse than US avg
Chittenden County 40
Bennington County, Vermont 39
US average 38
Unhealthy days / yr about average
Chittenden County 0
Bennington County, Vermont 0
US average 0
Other Counties in Vermont
Air quality comparison for nearby counties in Vermont.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Chittenden County.
Amador County, California
AQI 40 · 84.8% good
Anne Arundel County, Maryland
AQI 40 · 87.2% good
Arlington County, Virginia
AQI 40 · 84.8% good
Bergen County, New Jersey
AQI 40 · 71.1% good
Berkeley County, West Virginia
AQI 40 · 81.1% good
Billings County, North Dakota
AQI 40 · 80.3% good
What Chittenden 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 40 means for exposure. Health guidance
- See how Chittenden County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Chittenden County with its Vermont neighbours before drawing a conclusion about the region. All of Vermont
Based on 182 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 Chittenden County, Vermont? ▼
Chittenden County has a median Air Quality Index (AQI) of 40, rated "Good." 91.2% of monitored days (166 out of 182) had good air quality in 2025.
What is the main pollutant in Chittenden County? ▼
The primary pollutant in Chittenden County is Ozone (O3), which was the main AQI driver on 161 days (88% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Chittenden County have? ▼
In 2025, Chittenden County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 108.
Is the air quality in Chittenden County getting better or worse? ▼
Air quality in Chittenden County is improving based on 5-year trends (2020-2025). Best year: 2024 with 323 good days. Worst year: 2025 with 166 good days.
What does AQI 40 mean for health? ▼
Chittenden County's median AQI of 40 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 Chittenden County compare to other counties in Vermont? ▼
Chittenden County has 91.2% good air days. Nearby counties in Vermont: Bennington (82.9% good), Rutland (78.9% good), Windham (100.0% good).
What is the 90th percentile AQI in Chittenden County? ▼
The 90th percentile AQI for Chittenden County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 108 (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.