Bad Air Days in Fairfield County, Connecticut: 20 a Year

20 bad air days a year

Among the worst tenth of monitored US counties. Ranked 30 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (7% particle days).

The bad-air season here

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

What actually helps here

Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Sign up for EnviroFlash ozone alerts for this area during the worst months.

The record for Fairfield

In 2000 to 2009 this county averaged 32 bad days a year; in 2016 to 2025, 20. The air has improved. The worst recent year was 2016, with 23 bad days on 366 monitored days.

Date	AQI	Main pollutant
2023-06-07	242	PM2.5
2016-05-26	185	Ozone
2018-07-10	185	Ozone
2021-08-26	185	Ozone
2016-07-22	179	Ozone

An ordinary day in Fairfield

Across 3,651 monitored days from 2016 to 2025, the air in Fairfield County rated Good on 59% of them, less often than the 72% typical of monitored counties, and Moderate on 35%. The median day sat at AQI 46; one day in ten went above 78.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)55%2,006 days
ozone42%1,537 days
nitrogen dioxide3%107 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	236	108	21	2	44	174
2024	366	248	97	21	3	42	154
2023	365	210	135	20	8	46	242
2022	365	223	120	22	2	45	156
2021	363	225	119	19	6	46	185
2020	366	217	136	13	1	47	161
2019	365	221	123	21	3	46	161
2018	365	218	126	21	7	46	185
2017	365	208	141	16	4	46	179
2016	366	160	183	23	7	52	185
2015	365	152	183	30	6	53	177
2014	365	151	200	14	2	53	164
2013	365	136	204	25	6	55	185
2012	366	194	143	29	10	50	179
2011	365	257	88	20	8	41	190
2010	365	204	132	29	4	47	179

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

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