Median AQI
35
Good
Wisconsin · County air quality · 2025
Ozaukee County, Wisconsin
Median AQI 35 (Good). 80.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 35
- Median AQI
- 80.7%
- Good-air days
- 0
- Unhealthy days
- 54%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Ozaukee County's air is good on balance, cleaner than the median US county, a median AQI of 35 with 80.7% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 35
- median AQI · Good
- 80.7%
- days rated Good
- PM2.5
- main pollutant
- 54%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 140.
Data updated July 2026
- Good · 146 d · 80.7%
- Moderate · 31 d · 17.1%
- USG · 4 d · 2.2%
How did Ozaukee County's air break down in 2025?
Across 181 monitored days, 146 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 140 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 35 (Good).
Insights: Ozaukee County, Wisconsin. EPA monitors recorded a median Air Quality Index of 35 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 146 (81%) fell in the Good band (AQI 0–50), 31 (17%) registered Moderate readings, and 4 (2%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 140 (USG). Residents averaged about 24.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (110 days), Ozone (71 days). Across the 2020–2025 trend window, good days shifted by -123 and the median AQI moved -5 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 140, usg but never Unhealthy. Nearby counties show comparable readings: Ashland (85.6% good, AQI 39); Brown (79.0% good, AQI 37); Columbia (84.6% good, AQI 42); Dane (71.8% good, AQI 40); Dodge (76.4% good, AQI 39); Door (85.7% good, AQI 40).
Air Quality Summary
Good Days
80.7%
146 of 181 monitored days
5.7pp vs 75% target
Max AQI Recorded
140
USG
Health Grade
Good
90th-pct AQI 61
Ozaukee County, Good days share 80.7%
National avg
Share of monitored days at AQI 0-50 (Good band).
Ozaukee County, Unhealthy-or-worse share 0.0%
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
146
81%
Moderate
31
17%
USG
4
2%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Ozaukee County.
- PM2.5 · 110 days · 60.8%
- Ozone · 71 days · 39.2%
Health Impact Assessment
Good
Ozaukee County's air quality is rated Good based on 80.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 80.7% of monitored days in 2025, with a median AQI of 35. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 110 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Ozaukee County. Best year: 2024 (296 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 269 | 91 | 4 | 1 | 40 | 164 |
| 2021 | 241 | 116 | 7 | 0 | 43 | 129 |
| 2022 | 228 | 74 | 4 | 1 | 41 | 159 |
| 2023 | 219 | 126 | 14 | 2 | 45 | 210 |
| 2024 | 296 | 61 | 7 | 2 | 37 | 161 |
| 2025 | 146 | 31 | 4 | 0 | 35 | 140 |
How does Ozaukee County compare?
How Ozaukee County compares
Good-day share better than US avg
Ozaukee County 80.7%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI better than US avg
Ozaukee County 35
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Ozaukee County 0
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 Ozaukee County.
Androscoggin County, Maine
AQI 35 · 85.5% good
Asotin County, Washington
AQI 35 · 73.8% good
Benton County, Washington
AQI 35 · 88.9% good
Benzie County, Michigan
AQI 35 · 91.1% good
Brooke County, West Virginia
AQI 35 · 79.3% good
Bucks County, Pennsylvania
AQI 35 · 87.5% good
What Ozaukee County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 35 means for exposure. Health guidance
- See how Ozaukee County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Ozaukee 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 Ozaukee County, Wisconsin? ▼
Ozaukee County has a median Air Quality Index (AQI) of 35, rated "Good." 80.7% of monitored days (146 out of 181) had good air quality in 2025.
What is the main pollutant in Ozaukee County? ▼
The primary pollutant in Ozaukee County is Fine Particles (PM2.5), which was the main AQI driver on 110 days (61% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Ozaukee County have? ▼
In 2025, Ozaukee County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 140.
Is the air quality in Ozaukee County getting better or worse? ▼
Air quality in Ozaukee County is improving based on 5-year trends (2020-2025). Best year: 2024 with 296 good days. Worst year: 2025 with 146 good days.
What does AQI 35 mean for health? ▼
Ozaukee County's median AQI of 35 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 Ozaukee County compare to other counties in Wisconsin? ▼
Ozaukee County has 80.7% good air days. Nearby counties in Wisconsin: Ashland (85.6% good), Brown (79.0% good), Columbia (84.6% good), Dane (71.8% good), Dodge (76.4% good), Door (85.7% good).
What is the 90th percentile AQI in Ozaukee County? ▼
The 90th percentile AQI for Ozaukee County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 140 (USG).
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.