Median AQI
42
Good
Wisconsin · County air quality · 2025
Columbia County, Wisconsin
Median AQI 42 (Good). 84.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 84.6%
- Good-air days
- 0
- Unhealthy days
- 65%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Columbia County's air is good on balance, cleaner than the median US county, a median AQI of 42 with 84.6% of 91 monitored days in the Good band, driven mainly by Ozone.
- 42
- median AQI · Good
- 84.6%
- days rated Good
- Ozone
- main pollutant
- 65%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 108.
Data updated July 2026
- Good · 77 d · 84.6%
- Moderate · 13 d · 14.3%
- USG · 1 d · 1.1%
How did Columbia County's air break down in 2025?
Across 91 monitored days, 77 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 91 days monitored. Median AQI: 42 (Good).
Insights: Columbia County, Wisconsin. EPA monitors recorded a median Air Quality Index of 42 across 91 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 77 (85%) fell in the Good band (AQI 0–50), 13 (14%) registered Moderate readings, and 1 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 54, while the worst single-day peak hit 108 (USG). Residents averaged about 25.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (91 days). Across the 2020–2025 trend window, good days shifted by -110 and the median AQI moved +4 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 108, usg but never Unhealthy. Nearby counties show comparable readings: Ashland (85.6% good, AQI 39); Brown (79.0% good, AQI 37); 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
84.6%
77 of 91 monitored days
9.6pp vs 75% target
Max AQI Recorded
108
USG
Health Grade
Good
90th-pct AQI 54
Columbia County, Good days share 84.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Columbia 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 91 monitored days across EPA AQI categories.
Good
77
85%
Moderate
13
14%
USG
1
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 Columbia County.
- Ozone · 91 days · 100.0%
Health Impact Assessment
Good
Columbia County's air quality is rated Good based on 84.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 84.6% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 91 of 91 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Columbia County. Best year: 2022 (191 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 187 | 12 | 4 | 0 | 38 | 115 |
| 2021 | 181 | 27 | 0 | 0 | 40 | 100 |
| 2022 | 191 | 11 | 0 | 0 | 38 | 80 |
| 2023 | 133 | 52 | 16 | 2 | 44 | 159 |
| 2024 | 186 | 17 | 0 | 0 | 38 | 93 |
| 2025 | 77 | 13 | 1 | 0 | 42 | 108 |
How does Columbia County compare?
How Columbia County compares
Good-day share better than US avg
Columbia County 84.6%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI worse than US avg
Columbia County 42
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Columbia 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 Columbia County.
Adams County, Pennsylvania
AQI 42 · 73.8% good
Anderson County, Tennessee
AQI 42 · 91.0% good
Andrew County, Missouri
AQI 42 · 84.3% good
Armstrong County, Pennsylvania
AQI 42 · 68.1% good
Baldwin County, Alabama
AQI 42 · 72.2% good
Belmont County, Ohio
AQI 42 · 63.0% good
What Columbia County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 42 means for exposure. Health guidance
- See how Columbia County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Columbia County with its Wisconsin neighbours before drawing a conclusion about the region. All of Wisconsin
Based on 91 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 Columbia County, Wisconsin? ▼
Columbia County has a median Air Quality Index (AQI) of 42, rated "Good." 84.6% of monitored days (77 out of 91) had good air quality in 2025.
What is the main pollutant in Columbia County? ▼
The primary pollutant in Columbia County is Ozone (O3), which was the main AQI driver on 91 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Columbia County have? ▼
In 2025, Columbia County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 108.
Is the air quality in Columbia County getting better or worse? ▼
Air quality in Columbia County is worsening based on 5-year trends (2020-2025). Best year: 2022 with 191 good days. Worst year: 2025 with 77 good days.
What does AQI 42 mean for health? ▼
Columbia County's median AQI of 42 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 Columbia County compare to other counties in Wisconsin? ▼
Columbia County has 84.6% good air days. Nearby counties in Wisconsin: Ashland (85.6% good), Brown (79.0% 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 Columbia County? ▼
The 90th percentile AQI for Columbia County is 54, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 108 (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.