Michigan · County air quality · 2025

Marquette County, Michigan

Median AQI 19 (Good). 82.4% of monitored days rated Good, direct from EPA Air Quality System stations.

19
Median AQI
82.4%
Good-air days
6
Unhealthy days
62%
Cleaner than US counties

Marquette County's 2025 annual median AQI is 19 (Good), with 82.4% Good days

According to the U.S. EPA Air Quality System, Marquette County, Michigan posted a 2025 median AQI of 19 (Good) across 307 monitored days, with 82.4% rated Good and 6 unhealthy or worse. This is an annual comparison, not today's advisory.

Data source EPA Air Quality System (AQS)

Cleaner than US
Marquette County's 82.4% Good-day share places it cleaner than 62% of US counties in 2025.
Closest median-AQI peer
Cass County (95.9% Good, median AQI 19) is the closest nationwide median-AQI peer to Marquette County.
2024–2025 trend
Marquette County's floor-qualifying Good-day share is worsening from 2024 to 2025 (90.2% → 82.4%).
Median AQI
Median AQI: 19

According to the 2025 EPA AQS county release on PlainAirData, Marquette County, Michigan ranks #31 of 951 by median AQI (19) and #359 by good-day share (82.4%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.

Annual release change

What changed in the 2025 EPA annual release

2024 → 2025
  • Marquette County's peak single-day AQI rose from 67 to 193 between the 2024 and 2025 EPA annual releases, a change of +126 points.
  • Marquette County's Good-day share fell from 90.2% to 82.4% between the 2024 and 2025 EPA annual releases, a change of -7.8 percentage points.
  • Marquette County's Unhealthy-category days rose from 0 to 6 between the 2024 and 2025 EPA annual releases, a change of +6 days.

Compared against 224 monitored days in 2024 and 307 in 2025. These are arithmetic differences between two stored EPA annual summaries, not a cause claim or a live advisory.

National release changes Two-year CSV

Data updated August 2026

Marquette County AQI category distribution Stacked-segment bar showing the share of monitored days that fell in each EPA AQI category, Good, Moderate, USG, Unhealthy, Very Unhealthy, Hazardous, with median AQI marker. AQI category distribution 307 monitored days G M Median AQI 19 0 50 100 150 200 300 500 Marquette County
  • Good · 253 d · 82.4%
  • Moderate · 41 d · 13.4%
  • USG · 7 d · 2.3%
  • Unhealthy · 6 d · 2.0%

How did Marquette County's air break down in 2025?

Across 307 monitored days, 253 fell in the Good band (AQI 0–50) and 6 reached Unhealthy or worse. The worst single day peaked at AQI 193 (Unhealthy).

EPA AQS →
Marquette County, Good days share 82.4%
National avg

Share of monitored days at AQI 0-50 (Good band).

Marquette County, Unhealthy-or-worse share 19.5%
National avg

Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).

Where Marquette County sits nationally

COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Marquette County's Good-day share is 82.4% - cleaner than 62% of that comparison set.

Marquette County Good-day share vs. every US county

Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

82.4% Cleaner than 62% higher than 62% of 951 US counties

0.0%–5.0%: 0 US counties (0%). Below this entry. 5.0%–10.0%: 1 US counties (0%). Below this entry. 10.0%–15.0%: 4 US counties (0%). Below this entry. 15.0%–20.0%: 4 US counties (0%). Below this entry. 20.0%–25.0%: 1 US counties (0%). Below this entry. 25.0%–30.0%: 5 US counties (1%). Below this entry. 30.0%–35.0%: 9 US counties (1%). Below this entry. 35.0%–40.0%: 4 US counties (0%). Below this entry. 40.0%–45.0%: 16 US counties (2%). Below this entry. 45.0%–50.0%: 16 US counties (2%). Below this entry. 50.0%–55.0%: 32 US counties (3%). Below this entry. 55.0%–60.0%: 50 US counties (5%). Below this entry. 60.0%–65.0%: 77 US counties (8%). Below this entry. 65.0%–70.0%: 93 US counties (10%). Below this entry. 70.0%–75.0%: 109 US counties (11%). Below this entry. 75.0%–80.0%: 114 US counties (12%). Below this entry. 80.0%–85.0%: 123 US counties (13%). This entry sits in this band. 85.0%–90.0%: 99 US counties (10%). Above this entry. 90.0%–95.0%: 117 US counties (12%). Above this entry. 95.0%–100.0%: 70 US counties (7%). Above this entry. 100.0%–105.0%: 7 US counties (1%). Above this entry. This county 0.0% 100% every floor-qualified US county, bucketed by value

Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.

Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025

Pollutant Breakdown

Days where each pollutant was the primary driver of AQI readings in Marquette County.

Marquette County, Michigan criteria pollutant distribution Stratified-band visualization showing the share of monitored days each criteria pollutant (PM2.5, PM10, O3, NO2, CO) was the primary AQI driver. PM2.5 · 100.0% 0% 25% 50% 75% 100% Marquette County, Michigan · 307 monitored days Criteria pollutant column
  • PM2.5 · 307 days · 100.0%

2024 daily-monitor rhythm in Marquette County

Month-by-month median AQI from EPA day-level county monitors (224 reported days in 2024). Jul posted the highest typical readings (median AQI 32, peak 64); Nov was cleanest at median 11. Summer months (Jun–Aug) averaged median AQI 27 vs 12 in Dec–Feb.

0 5 10 15 20 25 30 35 May Jun Jul Aug Sep Oct Nov Dec 13 19 32 31 23 18 11 12
Marquette County median daily AQI by calendar month (2024, EPA daily county file)

Health Impact Assessment

Good

Marquette County's air quality is rated Good based on 82.4% good air days. There were 6 unhealthy days in 2025 when outdoor activity should be limited.

Air quality is acceptable most days, but 7 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 193. Sensitive groups should monitor real-time conditions at AirNow.gov.

The dominant pollutant is PM2.5, driving AQI on 307 of 307 monitored days.

5-Year Air Quality Trend

Air quality is worsening in Marquette County. Highest Good-day share: 2024 (90.2%, 202 of 224 monitored days).

Year Good Moderate USG Unhealthy Median AQI
2024 202 22 0 0 19
2025 253 41 7 6 19

How does Marquette County compare?

How Marquette County compares

Good-day share better than typical
Marquette County 82.4%
Cass County, Nebraska 95.9%
Typical US county 76.0%
Median AQI better than typical
Marquette County 19
Cass County, Nebraska 19
Typical US county 39
Unhealthy days / yr worse than typical
Marquette County 6
Cass County, Nebraska 0
Typical US county 1

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. Spotted a figure that looks wrong? Report a correction.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Marquette County, Michigan · 2020–2025

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Every figure on PlainAirData 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.