Bad Air Days in New Haven County, Connecticut: 12 a Year

12 bad air days a year

Among the worst tenth of monitored US counties. Ranked 61 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (9% particle days).

When the bad days come in New Haven

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

Is a purifier worth it 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 New Haven

In 2000 to 2009 this county averaged 27 bad days a year; in 2016 to 2025, 12. The air has improved. The worst recent year was 2016, with 14 bad days on 366 monitored days.

Date	AQI	Main pollutant
2023-06-07	208	PM2.5
2017-06-12	179	Ozone
2017-06-13	174	Ozone
2020-07-30	174	Ozone
2023-06-08	172	PM2.5

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in New Haven County rated Good on 62% of them, less often than the 72% typical of monitored counties, and Moderate on 34%. The median day sat at AQI 45; one day in ten went above 70.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)49%1,801 days
ozone47%1,735 days
nitrogen dioxide3%112 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	245	107	13	2	43	159
2024	366	260	94	12	1	41	156
2023	365	205	148	12	3	47	208
2022	365	230	128	7	0	44	133
2021	365	220	131	14	2	46	159
2020	366	210	143	13	2	46	174
2019	365	228	123	14	2	44	159
2018	365	220	131	14	2	44	156
2017	365	241	112	12	4	44	179
2016	366	211	141	14	3	47	164
2015	365	161	188	16	3	52	169
2014	365	174	183	8	0	51	126
2013	365	106	244	15	3	56	159
2012	366	120	220	26	7	54	187
2011	365	181	170	14	6	51	195
2010	364	204	143	17	0	46	140

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

Elsewhere in Connecticut

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.