EnviroNearby

Monroe County, Wisconsin air quality history

Daily Air Quality Index summaries from EPA monitors in Monroe, Wisconsin, 2012–2025.

68%
Good days in 2025
36
Median daily AQI, 2025
9
Days above 100 in 2025
305
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Monroe, Wisconsin on 305 days. 206 of those days (68%) were in the Good range, and the median daily AQI was 36. 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 305 days.

Years with fewer than 120 monitored days (2012, 2013) are shown in the table but left out of comparisons and trend statements.

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.

Share of monitored days in each AQI category, by year0%25%50%75%100%2012: Good 36 of 36 days20122013: Good 61 of 61 days20132021: Good 216 of 265 days2021: Moderate 49 of 265 days20212022: Good 295 of 364 days2022: Moderate 68 of 364 days2022: Unhealthy for Sensitive Groups 1 of 364 days20222023: Good 252 of 365 days2023: Moderate 108 of 365 days2023: Unhealthy for Sensitive Groups 3 of 365 days2023: Unhealthy 2 of 365 days20232024: Good 258 of 288 days2024: Moderate 30 of 288 days20242025: Good 206 of 305 days2025: Moderate 90 of 305 days2025: Unhealthy for Sensitive Groups 7 of 305 days2025: Unhealthy 2 of 305 days2025
  • 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 and 90th-percentile daily AQI, by year0501002012: 90th percentile AQI 192013: 90th percentile AQI 242021: 90th percentile AQI 562022: 90th percentile AQI 542023: 90th percentile AQI 602024: 90th percentile AQI 512025: 90th percentile AQI 622012: Median AQI 102013: Median AQI 132021: Median AQI 322022: Median AQI 322023: Median AQI 372024: Median AQI 232025: Median AQI 362012201320212022202320242025
  • 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.

PollutantDays as main pollutantShare of monitored days
Fine particles (PM2.5)305100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253052069072003662165PM2.5
2024288258300000235190PM2.5
202336525210832003760173PM2.5
20223642956810003254132PM2.5
2021265216490000325694PM2.5
2013616100000132444PM10
2012363600000101933PM10

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 2012–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem