Bad Air Days in Pennington County, South Dakota: 4 a Year

4 bad air days a year

About the middle of monitored US counties. Ranked 318 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 Pennington

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

Is a purifier worth it here?

Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.

The record for Pennington

In 2000 to 2009 this county averaged 2 bad days a year; in 2016 to 2025, 4. Not much has changed. The worst recent year was 2023, with 9 bad days on 365 monitored days.

Date	AQI	Main pollutant
2021-07-30	202	PM2.5
2023-05-18	172	PM2.5
2023-09-05	166	PM2.5
2023-09-06	158	PM2.5
2021-01-14	153	PM10

The air on a normal day

Across 3,646 monitored days from 2016 to 2025, the air in Pennington County rated Good on 70% of them, close to the 72% typical of monitored counties, and Moderate on 29%. The median day sat at AQI 37; one day in ten went above 65.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)58%2,112 days
coarse dust (PM10)38%1,388 days
nitrogen dioxide4%146 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	364	282	81	1	0	32	107
2024	366	248	114	4	0	36	111
2023	365	216	140	9	4	45	172
2022	363	238	123	2	0	40	116
2021	365	244	114	7	2	39	202
2020	366	264	102	0	0	35	92
2019	361	267	90	4	0	33	117
2018	365	263	100	2	0	36	118
2017	365	264	96	5	1	37	152
2016	366	284	81	1	0	33	101
2015	365	182	180	3	0	51	120
2014	365	258	107	0	0	38	89
2013	365	214	151	0	0	44	94
2012	366	259	107	0	0	38	79
2011	364	288	76	0	0	33	94
2010	365	298	67	0	0	33	93

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

Elsewhere in South Dakota

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.