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

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 661 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (36% particle days).

When the bad days come in Suffolk

Most bad days here fall in July and May and June. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 17 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2017, with 3 bad days on 365 monitored days.

Date	AQI	Main pollutant
2021-07-26	145	PM2.5
2017-05-17	119	Ozone
2021-06-05	112	Ozone
2022-07-24	112	Ozone
2018-05-02	108	Ozone

The air on a normal day

Across 3,653 monitored days from 2016 to 2025, the air in Suffolk County rated Good on 59% of them, less often than the 72% typical of monitored counties, and Moderate on 41%. The median day sat at AQI 45; one day in ten went above 62.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)76%2,768 days
ozone21%765 days
nitrogen dioxide3%115 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	279	84	2	0	37	106
2024	366	291	75	0	0	36	78
2023	365	231	134	0	0	44	99
2022	365	261	102	2	0	41	112
2021	365	237	125	3	0	44	145
2020	366	229	137	0	0	45	84
2019	365	224	141	0	0	46	87
2018	365	119	245	1	0	53	108
2017	365	98	264	3	0	56	119
2016	366	180	186	0	0	51	90
2015	365	141	223	1	0	53	126
2014	365	122	243	0	0	53	85
2013	365	125	235	5	0	54	122
2012	366	140	224	2	1	53	163
2011	365	100	262	3	0	55	123
2010	365	128	233	4	1	54	156

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

Elsewhere in Massachusetts

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, and on why a purifier does not touch ozone in smoke vs ozone.