Median AQI
39
Good
Massachusetts · County air quality · 2025
Hampshire County, Massachusetts
Median AQI 39 (Good). 81.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 81.1%
- Good-air days
- 0
- Unhealthy days
- 55%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Hampshire County's air is good on balance, cleaner than the median US county, a median AQI of 39 with 81.1% of 243 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 81.1%
- days rated Good
- Ozone
- main pollutant
- 55%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 117.
Data updated July 2026
- Good · 197 d · 81.1%
- Moderate · 42 d · 17.3%
- USG · 4 d · 1.6%
How did Hampshire County's air break down in 2025?
Across 243 monitored days, 197 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 117 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 39 (Good).
Insights: Hampshire County, Massachusetts. EPA monitors recorded a median Air Quality Index of 39 across 243 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 197 (81%) fell in the Good band (AQI 0–50), 42 (17%) registered Moderate readings, and 4 (2%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 57, while the worst single-day peak hit 117 (USG). Residents averaged about 24.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (182 days), PM2.5 (60 days), PM10 (1 days). Across the 2020–2025 trend window, good days shifted by -103 and the median AQI moved +0 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 117, usg but never Unhealthy. Nearby counties show comparable readings: Barnstable (92.5% good, AQI 38); 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).
Air Quality Summary
Good Days
81.1%
197 of 243 monitored days
6.1pp vs 75% target
Max AQI Recorded
117
USG
Health Grade
Good
90th-pct AQI 57
Hampshire County, Good days share 81.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Hampshire 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 243 monitored days across EPA AQI categories.
Good
197
81%
Moderate
42
17%
USG
4
2%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Hampshire County.
- Ozone · 182 days · 74.9%
- PM2.5 · 60 days · 24.7%
- PM10 · 1 days · 0.4%
Health Impact Assessment
Good
Hampshire County's air quality is rated Good based on 81.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 81.1% of monitored days in 2025, with a median AQI of 39. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 182 of 243 monitored days.
5-Year Air Quality Trend
Air quality is stable in Hampshire County. Best year: 2024 (324 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 300 | 66 | 0 | 0 | 39 | 84 |
| 2021 | 307 | 45 | 0 | 0 | 35 | 96 |
| 2022 | 267 | 98 | 0 | 0 | 42 | 97 |
| 2023 | 292 | 67 | 6 | 0 | 38 | 138 |
| 2024 | 324 | 40 | 2 | 0 | 35 | 112 |
| 2025 | 197 | 42 | 4 | 0 | 39 | 117 |
How does Hampshire County compare?
How Hampshire County compares
Good-day share better than US avg
Hampshire County 81.1%
Barnstable County, Massachusetts 92.5%
US average 76.5%
Median AQI worse than US avg
Hampshire County 39
Barnstable County, Massachusetts 38
US average 38
Unhealthy days / yr about average
Hampshire County 0
Barnstable 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 Hampshire County.
Ada County, Idaho
AQI 39 · 80.6% good
Aiken County, South Carolina
AQI 39 · 89.1% good
Albany County, New York
AQI 39 · 67.4% good
Alexander County, North Carolina
AQI 39 · 92.4% good
Ashland County, Wisconsin
AQI 39 · 85.6% good
Bennington County, Vermont
AQI 39 · 82.9% good
What Hampshire 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 39 means for exposure. Health guidance
- See how Hampshire County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Hampshire County with its Massachusetts neighbours before drawing a conclusion about the region. All of Massachusetts
Based on 243 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 Hampshire County, Massachusetts? ▼
Hampshire County has a median Air Quality Index (AQI) of 39, rated "Good." 81.1% of monitored days (197 out of 243) had good air quality in 2025.
What is the main pollutant in Hampshire County? ▼
The primary pollutant in Hampshire County is Ozone (O3), which was the main AQI driver on 182 days (75% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Hampshire County have? ▼
In 2025, Hampshire County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 117.
Is the air quality in Hampshire County getting better or worse? ▼
Air quality in Hampshire County is stable based on 5-year trends (2020-2025). Best year: 2024 with 324 good days. Worst year: 2025 with 197 good days.
What does AQI 39 mean for health? ▼
Hampshire County's median AQI of 39 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 Hampshire County compare to other counties in Massachusetts? ▼
Hampshire County has 81.1% good air days. Nearby counties in Massachusetts: Barnstable (92.5% good), Berkshire (71.6% good), Bristol (77.8% good), Dukes (95.2% good), Essex (77.0% good), Franklin (72.8% good).
What is the 90th percentile AQI in Hampshire County? ▼
The 90th percentile AQI for Hampshire County is 57, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 117 (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.