Median AQI
31
Good
Wisconsin · County air quality · 2025
Monroe County, Wisconsin
Median AQI 31 (Good). 75.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 31
- Median AQI
- 75.2%
- Good-air days
- 0
- Unhealthy days
- 41%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Monroe County's air is good on balance, more polluted than the median US county, a median AQI of 31 with 75.2% of 121 monitored days in the Good band, driven mainly by PM2.5.
- 31
- median AQI · Good
- 75.2%
- days rated Good
- PM2.5
- main pollutant
- 41%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 114.
Data updated July 2026
- Good · 91 d · 75.2%
- Moderate · 28 d · 23.1%
- USG · 2 d · 1.7%
How did Monroe County's air break down in 2025?
Across 121 monitored days, 91 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 114 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 121 days monitored. Median AQI: 31 (Good).
Insights: Monroe County, Wisconsin. EPA monitors recorded a median Air Quality Index of 31 across 121 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 91 (75%) fell in the Good band (AQI 0–50), 28 (23%) registered Moderate readings, and 2 (2%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 60, while the worst single-day peak hit 114 (USG). Residents averaged about 22.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (121 days). Across the 2021–2025 trend window, good days shifted by -125 and the median AQI moved -1 points, placing the multi-year trajectory at worsening. The worst single reading over the 2021–2025 window was AQI 114, 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
75.2%
91 of 121 monitored days
0.2pp vs 75% target
Max AQI Recorded
114
USG
Health Grade
Good
90th-pct AQI 60
Monroe County, Good days share 75.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Monroe 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 121 monitored days across EPA AQI categories.
Good
91
75%
Moderate
28
23%
USG
2
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 Monroe County.
- PM2.5 · 121 days · 100.0%
Health Impact Assessment
Good
Monroe County's air quality is rated Good based on 75.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 75.2% of monitored days in 2025, with a median AQI of 31. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 121 of 121 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Monroe County. Best year: 2022 (295 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2021 | 216 | 49 | 0 | 0 | 32 | 94 |
| 2022 | 295 | 68 | 1 | 0 | 32 | 132 |
| 2023 | 252 | 108 | 3 | 2 | 37 | 173 |
| 2024 | 258 | 30 | 0 | 0 | 23 | 90 |
| 2025 | 91 | 28 | 2 | 0 | 31 | 114 |
How does Monroe County compare?
How Monroe County compares
Good-day share worse than US avg
Monroe County 75.2%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI better than US avg
Monroe County 31
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Monroe 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 Monroe County.
Bannock County, Idaho
AQI 31 · 91.5% good
Clark County, Washington
AQI 31 · 89.3% good
Erie County, Pennsylvania
AQI 31 · 81.4% good
Honolulu County, Hawaii
AQI 31 · 95.0% good
Josephine County, Oregon
AQI 31 · 76.2% good
Montgomery County, Tennessee
AQI 31 · 84.7% good
What Monroe 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 31 means for exposure. Health guidance
- See how Monroe County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Monroe County with its Wisconsin neighbours before drawing a conclusion about the region. All of Wisconsin
Based on 121 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 Monroe County, Wisconsin? ▼
Monroe County has a median Air Quality Index (AQI) of 31, rated "Good." 75.2% of monitored days (91 out of 121) had good air quality in 2025.
What is the main pollutant in Monroe County? ▼
The primary pollutant in Monroe County is Fine Particles (PM2.5), which was the main AQI driver on 121 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Monroe County have? ▼
In 2025, Monroe County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 114.
Is the air quality in Monroe County getting better or worse? ▼
Air quality in Monroe County is worsening based on 5-year trends (2021-2025). Best year: 2022 with 295 good days. Worst year: 2025 with 91 good days.
What does AQI 31 mean for health? ▼
Monroe County's median AQI of 31 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 Monroe County compare to other counties in Wisconsin? ▼
Monroe County has 75.2% 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 Monroe County? ▼
The 90th percentile AQI for Monroe County is 60, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 114 (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.