Bad Air Days in Franklin County, Massachusetts: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 623 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (69% particle days).

When the bad days come in Franklin

Most bad days here fall in June and May and July. Averaged over 2016 to 2025.

What to buy, and what not to

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

The worst days on file

The worst recent year was 2023, with 6 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-07-01	154	PM2.5
2023-06-06	137	PM2.5
2023-06-07	117	PM2.5
2023-06-30	117	PM2.5
2016-05-26	115	Ozone

Most days, not the worst ones

Across 3,649 monitored days from 2016 to 2025, the air in Franklin County rated Good on 75% of them, close to the 72% typical of monitored counties, and Moderate on 25%. The median day sat at AQI 40; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)50%1,834 days
ozone50%1,815 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	364	280	81	3	0	38	114
2024	365	296	69	0	0	36	94
2023	365	246	113	6	1	43	154
2022	365	271	93	1	0	40	108
2021	365	228	137	0	0	44	99
2020	365	246	119	0	0	43	96
2019	364	281	83	0	0	40	89
2018	365	289	76	0	0	38	100
2017	365	300	65	0	0	37	90
2016	366	296	67	3	0	38	115
2015	365	233	132	0	0	44	100
2014	338	198	140	0	0	46	90

*2025 may be a partial year in EPA's file.

Massachusetts compared

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day.