What is the air quality in Keweenaw County, Michigan?

EPA monitors reported only 41 days for Keweenaw County in 2025, below the 100-day floor used for annual conclusions. Within that limited sample, the median AQI was 8 and 41 days were rated Good; this does not describe the full year.

What is the main pollutant in Keweenaw County?

The primary pollutant in Keweenaw County is Fine Particles (PM2.5), which was the main AQI driver on 41 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.

How many unhealthy air days does Keweenaw County have?

Among 41 reported days in 2025, 0 reached Unhealthy or worse. Because the record is below 100 monitored days, that count cannot establish how many unhealthy days occurred across the full year.

Is the air quality in Keweenaw County getting better or worse?

Air quality in Keweenaw County is stable across floor-qualifying years (2020-2024); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 99.1% (116 of 117 days). Lowest qualifying Good-day share: 2023 at 88.2% (105 of 119 days).

What does AQI 8 mean for health?

The median of the 41 reported days was AQI 8, in the "Good" category. The limited sample is not enough to assign the county a full-year health grade. See the AQI category guide for day-level meaning and EPA AirNow for current conditions.

How does Keweenaw County compare to other counties in Michigan?

Keweenaw County is not placed in county comparisons because its 41-day record is below the 100-day comparison floor.

What is the 90th percentile AQI in Keweenaw County?

The 90th percentile AQI for Keweenaw County is 16, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 31 (Good).

Michigan · County air quality · 2025

Keweenaw County, Michigan

Limited EPA sample: 41 monitored days, below the 100-day floor for a full-year verdict. The figures below describe only those reported days.

Compiled by PlainAirData · August 23, 2026

8
Sample median AQI: 100.0%
Good in sample: 0
Unhealthy in sample: 41
100-day comparison floor

Keweenaw County has only 41 EPA-monitored days in 2025, below the 100-day annual floor

According to the U.S. EPA Air Quality System, Keweenaw County, Michigan reported 41 monitored days in 2025. That sample is too thin for a full-year air-quality grade or peer ranking. Use the figures only as the reported-day record, and check AirNow for current conditions.

Data source EPA Air Quality System (AQS)

Monitored days: Keweenaw County reported 41 monitored days in 2025, below the 100-day floor: sample-only, not a full-year peer rank.
Sample median AQI: Sample median AQI: 8
Annual floor: Annual floor: 100

Keweenaw County's Good-day share rose from 88.2% to 98.3% between the 2023 and 2024 EPA annual releases, a change of +10.1 percentage points.
Keweenaw County's peak single-day AQI fell from 141 to 66 between the 2023 and 2024 EPA annual releases, a change of -75 points.
Keweenaw County's median AQI fell from 16 to 12 between the 2023 and 2024 EPA annual releases, a change of -4 points.

Data updated August 2026

Good · 41 d · 100.0%

How did Keweenaw County's reported sample break down in 2025?

Across 41 monitored days, 41 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 31 (Good).

EPA AQS →

Pollutant Breakdown

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

PM2.5 · 41 days · 100.0%

Sample Coverage and Health Context

Limited sample

Keweenaw County has no annual health grade because only 41 days were reported, below the 100-day floor. The 100.0% Good-day share describes only that sample.

Reported days do not reveal what happened during unmonitored parts of the year, including seasonal smoke, ozone, or inversion periods. Use these values as a description of the available EPA sample only, and check AirNow.gov for current health guidance.

The dominant pollutant is PM2.5, driving AQI on 41 of 41 monitored days.

5-Year Air Quality Trend

Air quality is stable in Keweenaw County. Highest Good-day share: 2020 (99.1%, 116 of 117 monitored days). The 2025 row is shown for transparency but excluded from the direction because it has fewer than 100 monitored days.

Year	Good	Moderate	USG	Median AQI	Max AQI
2020	116	0	1	13	124
2021	109	8	0	14	67
2022	119	3	0	12	58
2023	105	12	2	16	141
2024	118	2	0	12	66
2025	41	0	0	8	31

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 Keweenaw County, Michigan · 2020–2025 Accessed 2026-08-23

Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.

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.