Median AQI
18
Good
Michigan · County air quality · 2025
Marquette County, Michigan
Median AQI 18 (Good). 87.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 18
- Median AQI
- 87.0%
- Good-air days
- 1
- Unhealthy days
- 69%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Marquette County's air is good on balance, cleaner than the median US county, a median AQI of 18 with 87.0% of 123 monitored days in the Good band, driven mainly by PM2.5.
- 18
- median AQI · Good
- 87.0%
- days rated Good
- PM2.5
- main pollutant
- 69%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 183.
Data updated July 2026
- Good · 107 d · 87.0%
- Moderate · 15 d · 12.2%
- Unhealthy · 1 d · 0.8%
How did Marquette County's air break down in 2025?
Across 123 monitored days, 107 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 183 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 123 days monitored. Median AQI: 18 (Good).
Insights: Marquette County, Michigan. EPA monitors recorded a median Air Quality Index of 18 across 123 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 107 (87%) fell in the Good band (AQI 0–50), 15 (12%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 56, while the worst single-day peak hit 183 (Unhealthy). Residents averaged about 26.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (123 days). Across the 2024–2025 trend window, good days shifted by -95 and the median AQI moved -1 points, placing the multi-year trajectory at worsening. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Allegan (71.2% good, AQI 43); Bay (71.8% good, AQI 38); Benzie (91.1% good, AQI 35); Berrien (80.9% good, AQI 41); Cass (85.3% good, AQI 40); Clinton (90.2% good, AQI 39).
Air Quality Summary
Good Days
87.0%
107 of 123 monitored days
12.0pp vs 75% target
Max AQI Recorded
183
Unhealthy
Health Grade
Good
90th-pct AQI 56
Marquette County, Good days share 87.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Marquette County, Unhealthy-or-worse share 0.8%
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 123 monitored days across EPA AQI categories.
Good
107
87%
Moderate
15
12%
USG
0
0%
Unhealthy
1
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Marquette County.
- PM2.5 · 123 days · 100.0%
Health Impact Assessment
Good
Marquette County's air quality is rated Good based on 87.0% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 0 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 183. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 123 of 123 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Marquette County. Best year: 2024 (202 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2024 | 202 | 22 | 0 | 0 | 19 | 67 |
| 2025 | 107 | 15 | 0 | 1 | 18 | 183 |
How does Marquette County compare?
How Marquette County compares
Good-day share better than US avg
Marquette County 87.0%
Allegan County, Michigan 71.2%
US average 76.5%
Median AQI better than US avg
Marquette County 18
Allegan County, Michigan 43
US average 38
Unhealthy days / yr worse than US avg
Marquette County 1
Allegan County, Michigan 1
US average 0
Other Counties in Michigan
Air quality comparison for nearby counties in Michigan.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Marquette County.
Garfield County, Washington
AQI 18 · 95.9% good
Guayama County, Puerto Rico
AQI 18 · 100.0% good
Lewis County, Washington
AQI 18 · 93.3% good
Phillips County, Montana
AQI 18 · 94.2% good
St John County, Virgin Islands
AQI 18 · 100.0% good
Adams County, Washington
AQI 19 · 94.7% good
What Marquette County's air means for you
On most days the air here is fine, but PM2.5 drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 18 means for exposure. Health guidance
- See how Marquette County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Marquette County with its Michigan neighbours before drawing a conclusion about the region. All of Michigan
Based on 123 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 Marquette County, Michigan? ▼
Marquette County has a median Air Quality Index (AQI) of 18, rated "Good." 87.0% of monitored days (107 out of 123) had good air quality in 2025.
What is the main pollutant in Marquette County? ▼
The primary pollutant in Marquette County is Fine Particles (PM2.5), which was the main AQI driver on 123 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Marquette County have? ▼
In 2025, Marquette County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 183.
Is the air quality in Marquette County getting better or worse? ▼
Air quality in Marquette County is worsening based on 5-year trends (2024-2025). Best year: 2024 with 202 good days. Worst year: 2025 with 107 good days.
What does AQI 18 mean for health? ▼
Marquette County's median AQI of 18 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 Marquette County compare to other counties in Michigan? ▼
Marquette County has 87.0% good air days. Nearby counties in Michigan: Allegan (71.2% good), Bay (71.8% good), Benzie (91.1% good), Berrien (80.9% good), Cass (85.3% good), Clinton (90.2% good).
What is the 90th percentile AQI in Marquette County? ▼
The 90th percentile AQI for Marquette County is 56, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 183 (Unhealthy).
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.