Bad Air Days in Cook County, Minnesota: 2 a Year

2 bad air days a year

About the middle of monitored US counties. Ranked 489 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (100% particle days).

When the bad days come in Cook

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

What actually helps 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 record for Cook

In 2000 to 2009 this county averaged 0 bad days a year; in 2016 to 2025, 2. It has got worse. The worst recent year was 2025, with 12 bad days on 358 monitored days.

Date	AQI	Main pollutant
2025-07-30	201	PM2.5
2025-06-03	199	PM2.5
2025-07-29	172	PM2.5
2025-07-31	165	PM2.5
2025-08-01	160	PM2.5

Most days, not the worst ones

Across 3,459 monitored days from 2016 to 2025, the air in Cook County rated Good on 94% of them, more often than the 72% typical of monitored counties, and Moderate on 6%. The median day sat at AQI 16; one day in ten went above 40.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%3,459 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	358	315	31	12	8	16	201
2024	358	330	25	3	0	16	138
2023	346	298	47	1	0	13	120
2022	330	327	3	0	0	4	54
2021	328	306	18	4	1	9	153
2020	345	340	5	0	0	13	59
2019	334	317	17	0	0	22	81
2018	353	330	23	0	0	23	69
2017	351	332	19	0	0	24	62
2016	356	346	10	0	0	18	58
2015	258	248	10	0	0	26	91
2014	336	310	26	0	0	23	67
2013	270	231	39	0	0	29	74
2012	334	293	41	0	0	25	65
2011	307	235	71	1	0	31	126
2010	263	212	51	0	0	27	76

*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.