Median AQI
37
Good
Wisconsin · County air quality · 2025
Brown County, Wisconsin
Median AQI 37 (Good). 79.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 79.0%
- Good-air days
- 1
- Unhealthy days
- 49%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Brown County's air is good on balance, more polluted than the median US county, a median AQI of 37 with 79.0% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 37
- median AQI · Good
- 79.0%
- days rated Good
- PM2.5
- main pollutant
- 49%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 154.
Data updated July 2026
- Good · 143 d · 79.0%
- Moderate · 36 d · 19.9%
- USG · 1 d · 0.6%
- Unhealthy · 1 d · 0.6%
How did Brown County's air break down in 2025?
Across 181 monitored days, 143 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 154 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 37 (Good).
Insights: Brown County, Wisconsin. EPA monitors recorded a median Air Quality Index of 37 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 143 (79%) fell in the Good band (AQI 0–50), 36 (20%) registered Moderate readings, and 1 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 58, while the worst single-day peak hit 154 (Unhealthy). Residents averaged about 23.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (119 days), Ozone (62 days). Across the 2020–2025 trend window, good days shifted by -118 and the median AQI moved -2 points, placing the multi-year trajectory at improving. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Ashland (85.6% good, AQI 39); Columbia (84.6% good, AQI 42); Dane (71.8% good, AQI 40); Dodge (76.4% good, AQI 39); Door (85.7% good, AQI 40); Eau Claire (77.9% good, AQI 38).
Air Quality Summary
Good Days
79.0%
143 of 181 monitored days
4.0pp vs 75% target
Max AQI Recorded
154
Unhealthy
Health Grade
Good
90th-pct AQI 58
Brown County, Good days share 79.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Brown County, Unhealthy-or-worse share 0.6%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 181 monitored days across EPA AQI categories.
Good
143
79%
Moderate
36
20%
USG
1
1%
Unhealthy
1
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Brown County.
- PM2.5 · 119 days · 65.7%
- Ozone · 62 days · 34.3%
Health Impact Assessment
Good
Brown County's air quality is rated Good based on 79.0% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 1 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 154. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 119 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Brown County. Best year: 2024 (290 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 261 | 104 | 1 | 0 | 39 | 119 |
| 2021 | 231 | 131 | 3 | 0 | 43 | 125 |
| 2022 | 262 | 95 | 2 | 0 | 40 | 112 |
| 2023 | 216 | 136 | 8 | 5 | 44 | 179 |
| 2024 | 290 | 76 | 0 | 0 | 37 | 87 |
| 2025 | 143 | 36 | 1 | 1 | 37 | 154 |
How does Brown County compare?
How Brown County compares
Good-day share better than US avg
Brown County 79.0%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI better than US avg
Brown County 37
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr worse than US avg
Brown County 1
Ashland County, Wisconsin 1
US average 0
Other Counties in Wisconsin
Air quality comparison for nearby counties in Wisconsin.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Brown County.
Alachua County, Florida
AQI 37 · 90.1% good
Beltrami County, Minnesota
AQI 37 · 88.8% good
Benewah County, Idaho
AQI 37 · 74.6% good
Brevard County, Florida
AQI 37 · 89.7% good
Brown County, Indiana
AQI 37 · 94.5% good
Caldwell County, North Carolina
AQI 37 · 96.2% good
What Brown County's air means for you
On most days the air here is fine, but PM2.5 drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 37 means for exposure. Health guidance
- See how Brown County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Brown County with its Wisconsin neighbours before drawing a conclusion about the region. All of Wisconsin
Based on 181 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Brown County, Wisconsin? ▼
Brown County has a median Air Quality Index (AQI) of 37, rated "Good." 79.0% of monitored days (143 out of 181) had good air quality in 2025.
What is the main pollutant in Brown County? ▼
The primary pollutant in Brown County is Fine Particles (PM2.5), which was the main AQI driver on 119 days (66% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Brown County have? ▼
In 2025, Brown County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 154.
Is the air quality in Brown County getting better or worse? ▼
Air quality in Brown County is improving based on 5-year trends (2020-2025). Best year: 2024 with 290 good days. Worst year: 2025 with 143 good days.
What does AQI 37 mean for health? ▼
Brown County's median AQI of 37 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Brown County compare to other counties in Wisconsin? ▼
Brown County has 79.0% good air days. Nearby counties in Wisconsin: Ashland (85.6% good), Columbia (84.6% good), Dane (71.8% good), Dodge (76.4% good), Door (85.7% good), Eau Claire (77.9% good).
What is the 90th percentile AQI in Brown County? ▼
The 90th percentile AQI for Brown County is 58, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 154 (Unhealthy).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.