EnviroNearby

Franklin County, Massachusetts air quality history

Daily Air Quality Index summaries from EPA monitors in Franklin, Massachusetts, 1980–2025.

77%
Good days in 2025
38
Median daily AQI, 2025
3
Days above 100 in 2025
364
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Franklin, Massachusetts on 364 days. 280 of those days (77%) were in the Good range, and the median daily AQI was 38. That median is about the same as the typical monitored county in Massachusetts (median 38 across 13 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 201 days. Across the years with fuller monitoring, the share of Good days rose: an average of 68% in 2014–2016 versus 75% in 2023–2025.

Years with fewer than 120 monitored days (1980) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1980: Good 47 of 73 days1980: Moderate 14 of 73 days1980: Unhealthy for Sensitive Groups 7 of 73 days1980: Unhealthy 5 of 73 days19802014: Good 198 of 338 days2014: Moderate 140 of 338 days20142015: Good 233 of 365 days2015: Moderate 132 of 365 days20152016: Good 296 of 366 days2016: Moderate 67 of 366 days2016: Unhealthy for Sensitive Groups 3 of 366 days20162017: Good 300 of 365 days2017: Moderate 65 of 365 days20172018: Good 289 of 365 days2018: Moderate 76 of 365 days20182019: Good 281 of 364 days2019: Moderate 83 of 364 days20192020: Good 246 of 365 days2020: Moderate 119 of 365 days20202021: Good 228 of 365 days2021: Moderate 137 of 365 days20212022: Good 271 of 365 days2022: Moderate 93 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days20222023: Good 246 of 365 days2023: Moderate 113 of 365 days2023: Unhealthy for Sensitive Groups 5 of 365 days2023: Unhealthy 1 of 365 days20232024: Good 296 of 365 days2024: Moderate 69 of 365 days20242025: Good 280 of 364 days2025: Moderate 81 of 364 days2025: Unhealthy for Sensitive Groups 3 of 364 days2025
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001501980: 90th percentile AQI 1192014: 90th percentile AQI 642015: 90th percentile AQI 642016: 90th percentile AQI 572017: 90th percentile AQI 552018: 90th percentile AQI 572019: 90th percentile AQI 562020: 90th percentile AQI 602021: 90th percentile AQI 602022: 90th percentile AQI 592023: 90th percentile AQI 612024: 90th percentile AQI 562025: 90th percentile AQI 591980: Median AQI 412014: Median AQI 462015: Median AQI 442016: Median AQI 382017: Median AQI 372018: Median AQI 382019: Median AQI 402020: Median AQI 432021: Median AQI 442022: Median AQI 402023: Median AQI 432024: Median AQI 362025: Median AQI 381980201420152016201720182019202020212022202320242025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Ozone20155%
Fine particles (PM2.5)16345%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253642808130003859114Ozone
2024365296690000365694Ozone
202336524611351004361154PM2.5
20223652719310004059108PM2.5
20213652281370000446099PM2.5
20203652461190000436096PM2.5
2019364281830000405689Ozone
20183652897600003857100Ozone
2017365300650000375590Ozone
20163662966730003857115Ozone
201536523313200004464100PM2.5
20143381981400000466490PM2.5
1980734714750041119179Ozone

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in Massachusetts with a similar median AQI in 2025

All monitored counties in Massachusetts

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem