Bad Air Days in Chittenden County, Vermont: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 662 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (82% particle days).

When the bad days come in Chittenden

Most bad days here fall in June and July. 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.

The worst days on file

In 2000 to 2009 this county averaged 5 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2023, with 6 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-25	160	PM2.5
2025-07-26	156	PM2.5
2023-07-01	152	PM2.5
2023-06-26	135	PM2.5
2021-07-26	129	PM2.5

The air on a normal day

Across 3,653 monitored days from 2016 to 2025, the air in Chittenden County rated Good on 83% of them, more often than the 72% typical of monitored counties, and Moderate on 17%. The median day sat at AQI 39; one day in ten went above 54.

The pollutant setting the AQI on an ordinary day here:

ozone61%2,236 days
fine particles (PM2.5)39%1,411 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	320	41	4	1	38	156
2024	366	323	43	0	0	37	84
2023	365	259	100	6	2	42	160
2022	365	298	67	0	0	41	90
2021	365	288	76	1	0	40	129
2020	366	302	64	0	0	39	98
2019	365	306	59	0	0	39	82
2018	365	295	70	0	0	40	90
2017	365	312	53	0	0	37	74
2016	366	319	47	0	0	36	80
2015	365	278	87	0	0	39	100
2014	365	288	77	0	0	41	85
2013	365	260	104	1	0	42	133
2012	366	307	59	0	0	37	100
2011	365	250	113	2	0	43	105
2010	365	259	104	2	1	41	162

*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.