Bad Air Days in Brookings County, South Dakota: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 390 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (55% particle days).

When the bad days come in Brookings

Most bad days here fall in June 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.

Better or worse than it was

The worst recent year was 2021, with 8 bad days on 365 monitored days.

Date	AQI	Main pollutant
2021-07-29	236	PM2.5
2021-07-30	188	PM2.5
2023-07-15	162	PM2.5
2023-05-18	157	PM2.5
2025-06-01	154	PM2.5

Most days, not the worst ones

Across 3,651 monitored days from 2016 to 2025, the air in Brookings County rated Good on 79% of them, more often than the 72% typical of monitored counties, and Moderate on 20%. The median day sat at AQI 39; one day in ten went above 60.

The pollutant setting the AQI on an ordinary day here:

ozone65%2,363 days
fine particles (PM2.5)28%1,037 days
coarse dust (PM10)7%251 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	214	146	5	1	46	154
2024	366	292	72	2	0	36	111
2023	365	274	84	7	2	42	162
2022	364	320	44	0	0	36	87
2021	365	270	87	8	2	39	236
2020	366	305	61	0	0	39	87
2019	365	273	87	5	0	43	126
2018	365	297	67	1	0	38	101
2017	365	311	54	0	0	36	90
2016	365	329	35	1	0	35	101
2015	360	282	76	2	0	38	129
2014	362	308	53	1	0	36	108
2013	365	309	56	0	0	39	93
2012	366	267	98	1	0	40	112
2011	365	318	46	1	0	38	104
2010	365	306	59	0	0	37	97

*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.