Median AQI
36
Good
Wisconsin · County air quality · 2025
Marathon County, Wisconsin
Median AQI 36 (Good). 80.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 36
- Median AQI
- 80.0%
- Good-air days
- 0
- Unhealthy days
- 52%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Marathon County's air is good on balance, cleaner than the median US county, a median AQI of 36 with 80.0% of 180 monitored days in the Good band, driven mainly by PM2.5.
- 36
- median AQI · Good
- 80.0%
- days rated Good
- PM2.5
- main pollutant
- 52%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 113.
Data updated July 2026
- Good · 144 d · 80.0%
- Moderate · 34 d · 18.9%
- USG · 2 d · 1.1%
How did Marathon County's air break down in 2025?
Across 180 monitored days, 144 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 113 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 180 days monitored. Median AQI: 36 (Good).
Insights: Marathon County, Wisconsin. EPA monitors recorded a median Air Quality Index of 36 across 180 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 144 (80%) fell in the Good band (AQI 0–50), 34 (19%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 59, while the worst single-day peak hit 113 (USG). Residents averaged about 24.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (118 days), Ozone (62 days). Across the 2020–2025 trend window, good days shifted by -49 and the median AQI moved +5 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 113, 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
80.0%
144 of 180 monitored days
5.0pp vs 75% target
Max AQI Recorded
113
USG
Health Grade
Good
90th-pct AQI 59
Marathon County, Good days share 80.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Marathon 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 180 monitored days across EPA AQI categories.
Good
144
80%
Moderate
34
19%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Marathon County.
- PM2.5 · 118 days · 65.6%
- Ozone · 62 days · 34.4%
Health Impact Assessment
Good
Marathon County's air quality is rated Good based on 80.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 80.0% of monitored days in 2025, with a median AQI of 36. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 118 of 180 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Marathon County. Best year: 2024 (311 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 193 | 6 | 0 | 0 | 31 | 74 |
| 2021 | 191 | 9 | 0 | 0 | 36 | 87 |
| 2022 | 197 | 8 | 0 | 0 | 35 | 64 |
| 2023 | 168 | 39 | 8 | 1 | 41 | 166 |
| 2024 | 311 | 54 | 0 | 1 | 37 | 151 |
| 2025 | 144 | 34 | 2 | 0 | 36 | 113 |
How does Marathon County compare?
How Marathon County compares
Good-day share better than US avg
Marathon County 80.0%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI better than US avg
Marathon County 36
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Marathon 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 Marathon County.
Aroostook County, Maine
AQI 36 · 84.1% good
Berkeley County, South Carolina
AQI 36 · 92.2% good
Carter County, Kentucky
AQI 36 · 89.8% good
Claiborne County, Tennessee
AQI 36 · 96.3% good
Clark County, Illinois
AQI 36 · 92.1% good
Cobb County, Georgia
AQI 36 · 92.5% good
What Marathon 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 36 means for exposure. Health guidance
- See how Marathon County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Marathon County with its Wisconsin neighbours before drawing a conclusion about the region. All of Wisconsin
Based on 180 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 Marathon County, Wisconsin? ▼
Marathon County has a median Air Quality Index (AQI) of 36, rated "Good." 80.0% of monitored days (144 out of 180) had good air quality in 2025.
What is the main pollutant in Marathon County? ▼
The primary pollutant in Marathon County is Fine Particles (PM2.5), which was the main AQI driver on 118 days (66% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Marathon County have? ▼
In 2025, Marathon County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 113.
Is the air quality in Marathon County getting better or worse? ▼
Air quality in Marathon County is worsening based on 5-year trends (2020-2025). Best year: 2024 with 311 good days. Worst year: 2025 with 144 good days.
What does AQI 36 mean for health? ▼
Marathon County's median AQI of 36 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 Marathon County compare to other counties in Wisconsin? ▼
Marathon County has 80.0% 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 Marathon County? ▼
The 90th percentile AQI for Marathon County is 59, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 113 (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.