Bad Air Days in Windham County, Connecticut: 2 a Year

2 bad air days a year

About the middle of monitored US counties. Ranked 486 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (0% particle days).

When the bad days come in Windham

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

Is a purifier worth it here?

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 16 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2018, with 6 bad days on 358 monitored days.

Date	AQI	Main pollutant
2016-07-22	154	Ozone
2016-05-26	143	Ozone
2017-05-17	140	Ozone
2021-06-05	140	Ozone
2017-05-18	129	Ozone

Most days, not the worst ones

Across 3,583 monitored days from 2016 to 2025, the air in Windham County rated Good on 94% of them, more often than the 72% typical of monitored counties, and Moderate on 5%. The median day sat at AQI 35; one day in ten went above 46.

The pollutant setting the AQI on an ordinary day here:

ozone100%3,583 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	362	339	22	1	0	35	108
2024	359	340	17	2	0	34	122
2023	359	340	17	2	0	34	112
2022	355	338	17	0	0	35	93
2021	361	331	29	1	0	34	140
2020	356	345	11	0	0	35	87
2019	360	344	15	1	0	36	105
2018	358	332	20	6	0	34	129
2017	355	334	17	4	0	34	140
2016	358	331	23	4	1	35	154
2015	356	326	27	3	0	35	129
2014	354	328	25	1	0	34	101
2013	359	328	28	3	0	36	119
2012	358	317	32	9	0	34	147
2011	212	193	16	3	0	34	140
2010	326	282	39	5	0	36	122

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

Nearby counties on file

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.