Median AQI
43
Good
Massachusetts · County air quality · 2025
Norfolk County, Massachusetts
Median AQI 43 (Good). 79.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 43
- Median AQI
- 79.4%
- Good-air days
- 0
- Unhealthy days
- 50%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Norfolk County's air is good on balance, cleaner than the median US county, a median AQI of 43 with 79.4% of 243 monitored days in the Good band, driven mainly by Ozone.
- 43
- median AQI · Good
- 79.4%
- days rated Good
- Ozone
- main pollutant
- 50%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 126.
Data updated July 2026
- Good · 193 d · 79.4%
- Moderate · 48 d · 19.8%
- USG · 2 d · 0.8%
How did Norfolk County's air break down in 2025?
Across 243 monitored days, 193 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 126 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 43 (Good).
Insights: Norfolk County, Massachusetts. EPA monitors recorded a median Air Quality Index of 43 across 243 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 193 (79%) fell in the Good band (AQI 0–50), 48 (20%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 62, while the worst single-day peak hit 126 (USG). Residents averaged about 23.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (197 days), PM2.5 (46 days). Across the 2020–2025 trend window, good days shifted by -137 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 126, 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
79.4%
193 of 243 monitored days
4.4pp vs 75% target
Max AQI Recorded
126
USG
Health Grade
Good
90th-pct AQI 62
Norfolk County, Good days share 79.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Norfolk 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
193
79%
Moderate
48
20%
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 Norfolk County.
- Ozone · 197 days · 81.1%
- PM2.5 · 46 days · 18.9%
Health Impact Assessment
Good
Norfolk County's air quality is rated Good based on 79.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 79.4% 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 197 of 243 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Norfolk County. Best year: 2020 (330 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 330 | 36 | 0 | 0 | 34 | 74 |
| 2021 | 280 | 82 | 3 | 0 | 37 | 133 |
| 2022 | 304 | 60 | 1 | 0 | 40 | 105 |
| 2023 | 276 | 85 | 4 | 0 | 41 | 136 |
| 2024 | 319 | 47 | 0 | 0 | 39 | 90 |
| 2025 | 193 | 48 | 2 | 0 | 43 | 126 |
How does Norfolk County compare?
How Norfolk County compares
Good-day share better than US avg
Norfolk County 79.4%
Barnstable County, Massachusetts 92.5%
US average 76.5%
Median AQI worse than US avg
Norfolk County 43
Barnstable County, Massachusetts 38
US average 38
Unhealthy days / yr about average
Norfolk 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 Norfolk 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 Norfolk 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 Norfolk County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Norfolk 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 Norfolk County, Massachusetts? ▼
Norfolk County has a median Air Quality Index (AQI) of 43, rated "Good." 79.4% of monitored days (193 out of 243) had good air quality in 2025.
What is the main pollutant in Norfolk County? ▼
The primary pollutant in Norfolk County is Ozone (O3), which was the main AQI driver on 197 days (81% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Norfolk County have? ▼
In 2025, Norfolk County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 126.
Is the air quality in Norfolk County getting better or worse? ▼
Air quality in Norfolk County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 330 good days. Worst year: 2025 with 193 good days.
What does AQI 43 mean for health? ▼
Norfolk 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 Norfolk County compare to other counties in Massachusetts? ▼
Norfolk County has 79.4% 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 Norfolk County? ▼
The 90th percentile AQI for Norfolk County is 62, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 126 (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.