Bad Air Days in Dane County, Wisconsin: 4 a Year

4 bad air days a year

About the middle of monitored US counties. Ranked 316 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (49% particle days).

When the bad days come in Dane

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

The worst days on file

In 2000 to 2009 this county averaged 10 bad days a year; in 2016 to 2025, 4. The air has improved. The worst recent year was 2023, with 24 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	268	PM2.5
2023-06-29	209	PM2.5
2023-06-27	208	PM2.5
2025-07-31	170	PM2.5
2023-07-24	154	PM2.5

Most days, not the worst ones

Across 3,641 monitored days from 2016 to 2025, the air in Dane County rated Good on 63% of them, less often than the 72% typical of monitored counties, and Moderate on 36%. The median day sat at AQI 44; one day in ten went above 65.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)68%2,480 days
ozone32%1,150 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	246	113	6	1	41	170
2024	366	264	102	0	0	42	93
2023	365	184	157	24	4	50	268
2022	365	236	129	0	0	45	91
2021	365	199	165	1	0	48	101
2020	366	222	142	2	0	44	112
2019	365	239	126	0	0	43	93
2018	365	215	148	2	0	46	112
2017	358	241	117	0	0	42	86
2016	361	246	115	0	0	41	100
2015	347	224	122	1	0	44	106
2014	365	199	164	2	0	47	112
2013	365	182	183	0	0	51	93
2012	355	158	187	10	2	52	154
2011	359	182	176	1	0	50	106
2010	354	117	233	4	0	55	125

*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.