Median AQI
38
Good
Massachusetts · County air quality · 2025
Barnstable County, Massachusetts
Median AQI 38 (Good). 92.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 92.5%
- Good-air days
- 0
- Unhealthy days
- 82%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Barnstable County's air is good on balance, cleaner than most US counties, a median AQI of 38 with 92.5% of 241 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 92.5%
- days rated Good
- Ozone
- main pollutant
- 82%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 129.
Data updated July 2026
- Good · 223 d · 92.5%
- Moderate · 15 d · 6.2%
- USG · 3 d · 1.2%
How did Barnstable County's air break down in 2025?
Across 241 monitored days, 223 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 129 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 241 days monitored. Median AQI: 38 (Good).
Insights: Barnstable County, Massachusetts. EPA monitors recorded a median Air Quality Index of 38 across 241 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 223 (93%) fell in the Good band (AQI 0–50), 15 (6%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 48, while the worst single-day peak hit 129 (USG). Residents averaged about 27.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (241 days). Across the 2020–2025 trend window, good days shifted by -116 and the median AQI moved +2 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 129, usg but never Unhealthy. Nearby counties show comparable readings: Berkshire (71.6% good, AQI 41); Bristol (77.8% good, AQI 41); Dukes (95.2% good, AQI 37); Essex (77.0% good, AQI 42); Franklin (72.8% good, AQI 40); Hampden (72.2% good, AQI 41).
Air Quality Summary
Good Days
92.5%
223 of 241 monitored days
17.5pp vs 75% target
Max AQI Recorded
129
USG
Health Grade
Excellent
90th-pct AQI 48
Barnstable County, Good days share 92.5%
National avg
Share of monitored days at AQI 0-50 (Good band).
Barnstable 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 241 monitored days across EPA AQI categories.
Good
223
93%
Moderate
15
6%
USG
3
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 Barnstable County.
- Ozone · 241 days · 100.0%
Health Impact Assessment
Excellent
Barnstable County's air quality is rated Excellent based on 92.5% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 92.5% 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 241 of 241 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Barnstable County. Best year: 2022 (341 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 339 | 10 | 2 | 0 | 36 | 108 |
| 2021 | 331 | 25 | 3 | 0 | 36 | 126 |
| 2022 | 341 | 19 | 0 | 0 | 36 | 93 |
| 2023 | 331 | 24 | 3 | 0 | 37 | 140 |
| 2024 | 333 | 19 | 1 | 0 | 36 | 101 |
| 2025 | 223 | 15 | 3 | 0 | 38 | 129 |
How does Barnstable County compare?
How Barnstable County compares
Good-day share better than US avg
Barnstable County 92.5%
Berkshire County, Massachusetts 71.6%
US average 76.5%
Median AQI about average
Barnstable County 38
Berkshire County, Massachusetts 41
US average 38
Unhealthy days / yr about average
Barnstable County 0
Berkshire County, Massachusetts 0
US average 0
Other Counties in Massachusetts
Air quality comparison for nearby counties in Massachusetts.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Barnstable 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
Bay County, Michigan
AQI 38 · 71.8% good
Becker County, Minnesota
AQI 38 · 84.7% good
What Barnstable 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 Barnstable County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Barnstable County with its Massachusetts neighbours before drawing a conclusion about the region. All of Massachusetts
Based on 241 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 Barnstable County, Massachusetts? ▼
Barnstable County has a median Air Quality Index (AQI) of 38, rated "Good." 92.5% of monitored days (223 out of 241) had good air quality in 2025.
What is the main pollutant in Barnstable County? ▼
The primary pollutant in Barnstable County is Ozone (O3), which was the main AQI driver on 241 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Barnstable County have? ▼
In 2025, Barnstable County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 129.
Is the air quality in Barnstable County getting better or worse? ▼
Air quality in Barnstable County is worsening based on 5-year trends (2020-2025). Best year: 2022 with 341 good days. Worst year: 2025 with 223 good days.
What does AQI 38 mean for health? ▼
Barnstable 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 Barnstable County compare to other counties in Massachusetts? ▼
Barnstable County has 92.5% good air days. Nearby counties in Massachusetts: Berkshire (71.6% good), Bristol (77.8% good), Dukes (95.2% good), Essex (77.0% good), Franklin (72.8% good), Hampden (72.2% good).
What is the 90th percentile AQI in Barnstable County? ▼
The 90th percentile AQI for Barnstable County is 48, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 129 (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.