Brown County, Wisconsin air quality history

Daily Air Quality Index summaries from EPA monitors in Brown, Wisconsin, 1980–2025.

73%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

365

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Brown, Wisconsin on 365 days. 267 of those days (73%) were in the Good range, and the median daily AQI was 37. That median is about the same as the typical monitored county in Wisconsin (median 38 across 29 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 256 days. Across the years with fuller monitoring, the share of Good days fell: an average of 90% in 1980–1982 versus 71% in 2023–2025.

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)	256	70%
Ozone	109	30%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Very Unhealthy	Median AQI	90th pct.	Max AQI	Main pollutant
2025	365	267	87	4	7	0	37	66	175	PM2.5
2024	366	290	76	0	0	0	37	58	87	PM2.5
2023	365	216	136	8	5	0	44	74	179	PM2.5
2022	359	262	95	2	0	0	40	59	112	PM2.5
2021	365	231	131	3	0	0	43	67	125	PM2.5
2020	366	261	104	1	0	0	39	59	119	PM2.5
2019	361	265	96	0	0	0	40	58	97	PM2.5
2018	360	262	97	1	0	0	42	61	105	PM2.5
2017	360	288	72	0	0	0	38	57	92	PM2.5
2016	366	282	81	3	0	0	36	59	112	PM2.5
2015	362	237	124	1	0	0	42	62	122	PM2.5
2014	365	217	146	2	0	0	44	67	119	PM2.5
2013	365	230	134	1	0	0	44	63	108	PM2.5
2012	366	210	141	14	1	0	47	74	179	PM2.5
2011	364	135	222	7	0	0	55	80	147	PM2.5
2010	356	202	147	7	0	0	46	74	127	PM2.5
2009	361	196	157	8	0	0	47	77	131	PM2.5
2008	352	156	190	6	0	0	53	76	143	PM2.5
2007	356	171	174	11	0	0	51	82	147	PM2.5
2006	246	160	81	4	1	0	42	74	152	Ozone
2005	244	146	86	11	1	0	44	84	182	Ozone
2004	245	169	73	3	0	0	40	70	126	Ozone
2003	237	151	78	5	2	1	44	77	204	Ozone
2002	244	157	75	10	2	0	43	84	156	Ozone
2001	240	154	72	9	5	0	44	87	185	Ozone
2000	247	170	70	6	1	0	41	78	154	Ozone
1999	244	148	81	12	3	0	43	85	172	Ozone
1998	183	140	36	5	2	0	42	74	161	Ozone
1997	184	149	30	4	1	0	38	61	182	Ozone
1996	179	145	22	7	5	0	41	77	182	Ozone
1995	179	143	27	7	2	0	38	80	185	Ozone
1994	178	159	17	2	0	0	36	51	133	Ozone
1993	202	190	10	2	0	0	33	44	119	Ozone
1992	214	188	23	3	0	0	30	54	108	Ozone
1991	210	176	25	8	1	0	32	71	164	Ozone
1990	213	177	33	3	0	0	33	58	136	Ozone
1989	249	202	33	11	3	0	35	80	190	Ozone
1988	260	208	30	15	7	0	33	84	169	Ozone
1987	258	214	34	8	2	0	36	71	161	Ozone
1986	242	200	39	3	0	0	32	61	119	Ozone
1985	214	163	39	9	3	0	38	87	177	Ozone
1984	176	150	20	6	0	0	37	64	143	Ozone
1983	194	152	25	12	5	0	37	87	187	Ozone
1982	180	162	14	4	0	0	31	51	122	Ozone
1981	264	247	9	8	0	0	29	47	150	Ozone
1980	269	229	27	9	4	0	25	80	164	Ozone

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 Wisconsin with a similar median AQI in 2025

All monitored counties in Wisconsin

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem