Bad Air Days in Washington County, Minnesota: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 644 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 Washington

Most bad days here fall in June and May. 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 6 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2023, with 8 bad days on 240 monitored days.

Date	AQI	Main pollutant
2023-06-20	140	Ozone
2023-06-22	140	Ozone
2023-06-09	136	Ozone
2023-06-21	129	Ozone
2021-06-10	119	Ozone

The air on a normal day

Across 2,747 monitored days from 2016 to 2025, the air in Washington County rated Good on 78% of them, more often than the 72% typical of monitored counties, and Moderate on 22%. The median day sat at AQI 40; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

ozone69%1,905 days
fine particles (PM2.5)27%736 days
coarse dust (PM10)4%106 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Median AQI	Highest AQI
2025*	236	224	12	0	34	84
2024	246	241	5	0	35	58
2023	240	194	38	8	42	140
2022	227	212	15	0	36	90
2021	227	205	21	1	35	119
2020	215	210	5	0	33	77
2019	260	192	68	0	37	87
2018	365	158	207	0	53	100
2017	365	218	147	0	46	97
2016	366	275	91	0	36	89
2015	365	203	160	2	46	122
2014	365	229	136	0	44	98
2013	365	202	163	0	47	98
2012	322	168	152	2	49	107
2011	192	180	11	1	37	129
2010	180	163	16	1	40	105

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

Minnesota compared

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.