Brown County, South Dakota air quality history

Daily Air Quality Index summaries from EPA monitors in Brown, South Dakota, 1985–2025.

84%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

360

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Brown, South Dakota on 360 days. 301 of those days (84%) were in the Good range, and the median daily AQI was 27. That median is lower than the typical monitored county in South Dakota (median 35.5 across 10 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 276 days. Across the years with fuller monitoring, the share of Good days rose: an average of 69% in 2001–2003 versus 83% in 2023–2025.

Years with fewer than 120 monitored days (1986, 1987, 2000, 2010, 2014, 2016…) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median daily AQI
90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

Pollutant	Days as main pollutant	Share of monitored days
Fine particles (PM2.5)	276	77%
Coarse particles (PM10)	84	23%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Very Unhealthy	Hazardous	Median AQI	90th pct.	Max AQI	Main pollutant
2025	360	301	53	6	0	0	0	27	56	115	PM2.5
2024	357	306	47	4	0	0	0	24	54	118	PM2.5
2023	365	289	68	7	1	0	0	29	60	166	PM2.5
2022	350	325	25	0	0	0	0	23	45	93	PM2.5
2021	356	301	52	0	2	1	0	26	58	208	PM2.5
2020	364	308	56	0	0	0	0	28	54	78	PM2.5
2019	122	104	18	0	0	0	0	25	53	80	PM2.5
2018	121	104	15	1	0	0	1	32	53	421	PM2.5
2017	122	108	14	0	0	0	0	31	52	97	PM2.5
2016	119	104	15	0	0	0	0	26	53	79	PM2.5
2015	121	102	19	0	0	0	0	32	54	94	PM2.5
2014	119	103	16	0	0	0	0	29	53	85	PM2.5
2013	121	90	31	0	0	0	0	34	60	77	PM2.5
2012	123	86	37	0	0	0	0	37	58	80	PM2.5
2011	122	94	28	0	0	0	0	33	59	70	PM2.5
2010	119	80	39	0	0	0	0	41	61	92	PM2.5
2009	122	86	36	0	0	0	0	39	58	90	PM2.5
2008	122	90	32	0	0	0	0	38	58	89	PM2.5
2007	121	86	35	0	0	0	0	42	56	74	PM2.5
2006	122	79	43	0	0	0	0	40	58	75	PM2.5
2005	122	75	47	0	0	0	0	43	65	83	PM2.5
2004	123	85	38	0	0	0	0	39	59	86	PM2.5
2003	121	80	41	0	0	0	0	43	60	74	PM2.5
2002	122	88	34	0	0	0	0	38	57	71	PM2.5
2001	127	87	40	0	0	0	0	40	61	82	PM2.5
2000	103	73	30	0	0	0	0	40	60	80	PM2.5
1987	83	81	2	0	0	0	0	21	40	54	PM10
1986	97	94	3	0	0	0	0	21	41	54	PM10
1985	65	62	3	0	0	0	0	26	42	64	PM10

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in South Dakota with a similar median AQI in 2025

All monitored counties in South Dakota

Source: U.S. EPA AirData, “Annual AQI by County” files for 1985–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem