Median AQI
38
Good
Massachusetts · County air quality · 2025
Franklin County, Massachusetts
Median AQI 38 (Good). 76.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 76.9%
- Good-air days
- 0
- Unhealthy days
- 48%
- Cleaner than US counties
Franklin County's 2025 annual median AQI is 38 (Good), with 76.9% Good days
According to the U.S. EPA Air Quality System, Franklin County, Massachusetts posted a 2025 median AQI of 38 (Good) across 364 monitored days, with 76.9% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Franklin County's 76.9% Good-day share places it cleaner than 48% of US counties in 2025.
- Closest median-AQI peer
- Adams County (94.7% Good, median AQI 38) is the closest nationwide median-AQI peer to Franklin County.
- 2020–2025 trend
- Franklin County's floor-qualifying Good-day share is improving from 2020 to 2025 (67.4% → 76.9%).
- Median AQI
- Median AQI: 38
The verdict
According to EPA Air Quality System monitoring data, Franklin County's air is good on balance, more polluted than the median US county, a median AQI of 38 with 76.9% of 364 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 76.9%
- days rated Good
- Ozone
- main pollutant
- 48%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 114.
Annual release change
What changed in the 2025 EPA annual release
- Franklin County's Good-day share fell from 81.1% to 76.9% between the 2024 and 2025 EPA annual releases, a change of -4.2 percentage points.
- Franklin County's peak single-day AQI rose from 94 to 114 between the 2024 and 2025 EPA annual releases, a change of +20 points.
Data updated August 2026
- Good · 280 d · 76.9%
- Moderate · 81 d · 22.3%
- USG · 3 d · 0.8%
How did Franklin County's air break down in 2025?
Across 364 monitored days, 280 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 114 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 364 days monitored. Median AQI: 38 (Good).
Insights: Franklin County, Massachusetts. EPA monitors recorded a median Air Quality Index of 38 across 364 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 280 (77%) fell in the Good band (AQI 0–50), 81 (22%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 59, while the worst single-day peak hit 114 (USG). Residents averaged about 23.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (201 days), PM2.5 (163 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +9.5 points and the median AQI moved -5 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 114, usg but never Unhealthy. Nearby counties show comparable readings: Barnstable (93.7% good, AQI 36); Berkshire (78.1% good, AQI 38); Bristol (83.8% good, AQI 38); Dukes (95.9% good, AQI 35); Essex (81.1% good, AQI 40); Hampden (77.0% good, AQI 39).
Air Quality Summary
Good Days
76.9%
280 of 364 monitored days
1.9pp vs 75% target
Max AQI Recorded
114
USG
Health Grade
Good
90th-pct AQI 59
Franklin County, Good days share 76.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Franklin 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 364 monitored days across EPA AQI categories.
Good
280
77%
Moderate
81
22%
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 Franklin County.
- Ozone · 201 days · 55.2%
- PM2.5 · 163 days · 44.8%
Health Impact Assessment
Good
Franklin County's air quality is rated Good based on 76.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 76.9% 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 201 of 364 monitored days.
5-Year Air Quality Trend
Air quality is improving in Franklin County. Highest Good-day share: 2024 (81.1%, 296 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 246 | 119 | 0 | 0 | 43 | 96 |
| 2021 | 228 | 137 | 0 | 0 | 44 | 99 |
| 2022 | 271 | 93 | 1 | 0 | 40 | 108 |
| 2023 | 246 | 113 | 5 | 1 | 43 | 154 |
| 2024 | 296 | 69 | 0 | 0 | 36 | 94 |
| 2025 | 280 | 81 | 3 | 0 | 38 | 114 |
How does Franklin County compare?
How Franklin County compares
Good-day share better than typical
Franklin County 76.9%
Adams County, Illinois 94.7%
Typical US county 76.0%
Median AQI better than typical
Franklin County 38
Adams County, Illinois 38
Typical US county 39
Unhealthy days / yr better than typical
Franklin County 0
Adams County, Illinois 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Franklin County (38), not geographic neighbors.
Adams County, Illinois
Median AQI 38 · 94.7% Good-day share
Albemarle County, Virginia
Median AQI 38 · 81.0% Good-day share
Alexander County, North Carolina
Median AQI 38 · 93.5% Good-day share
Amador County, California
Median AQI 38 · 87.4% Good-day share
Anoka County, Minnesota
Median AQI 38 · 74.1% Good-day share
Avery County, North Carolina
Median AQI 38 · 92.3% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Blair County, Pennsylvania
76.9% Good-day share · median AQI 40
Hampden County, Massachusetts
77.0% Good-day share · median AQI 39
White Pine County, Nevada
77.0% Good-day share · median AQI 45
DeKalb County, Alabama
77.3% Good-day share · median AQI 41
La Paz County, Arizona
76.6% Good-day share · median AQI 44
York County, South Carolina
76.5% Good-day share · median AQI 43
Massachusetts counties on the map
Geographic containment only, other monitored counties in Massachusetts, independent of AQI or pollutant match.
What Franklin 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 Franklin County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Franklin County with its Massachusetts neighbours before drawing a conclusion about the region. All of Massachusetts
Based on 364 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Franklin County, Massachusetts? ▼
Franklin County has a median Air Quality Index (AQI) of 38, rated "Good." 76.9% of monitored days (280 out of 364) had good air quality in 2025.
What is the main pollutant in Franklin County? ▼
The primary pollutant in Franklin County is Ozone (O3), which was the main AQI driver on 201 days (55% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Franklin County have? ▼
In 2025, Franklin County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 114.
Is the air quality in Franklin County getting better or worse? ▼
Air quality in Franklin County is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2024 at 81.1% (296 of 365 days). Lowest qualifying Good-day share: 2021 at 62.5% (228 of 365 days).
What does AQI 38 mean for health? ▼
Franklin County's median AQI of 38 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Franklin County compare to other counties in Massachusetts? ▼
Franklin County has 76.9% good air days. Nearby counties in Massachusetts: Barnstable (93.7% good), Berkshire (78.1% good), Bristol (83.8% good), Dukes (95.9% good), Essex (81.1% good), Hampden (77.0% good).
What is the 90th percentile AQI in Franklin County? ▼
The 90th percentile AQI for Franklin County is 59, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 114 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Franklin County, Massachusetts · 2020–2025
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Every figure on PlainAirData 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.