Bad Air Days in Fond du Lac County, Wisconsin: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 515 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 Fond du Lac

Most bad days here fall in June and May and April. 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 12 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 4 bad days on 204 monitored days.

Date	AQI	Main pollutant
2023-05-30	122	Ozone
2020-06-08	115	Ozone
2020-06-18	112	Ozone
2016-04-17	108	Ozone
2016-06-19	108	Ozone

The air on a normal day

Across 2,095 monitored days from 2016 to 2025, the air in Fond du Lac County rated Good on 90% of them, more often than the 72% typical of monitored counties, and Moderate on 9%. The median day sat at AQI 38; one day in ten went above 52.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,095 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	199	182	17	0	0	37	80
2024	205	190	15	0	0	38	77
2023	204	162	38	4	0	41	122
2022	203	193	9	1	0	36	108
2021	208	178	30	0	0	39	90
2020	205	194	9	2	0	36	115
2019	202	195	7	0	0	36	100
2018	244	213	30	1	0	39	101
2017	236	216	20	0	0	37	93
2016	189	165	21	3	0	38	108
2015	194	165	29	0	0	40	97
2014	194	165	27	2	0	40	105
2013	189	167	22	0	0	39	90
2012	207	151	41	15	1	42	192
2011	198	176	15	7	0	40	140
2010	207	190	16	1	0	39	101

*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.