Keweenaw County, Michigan air quality history

Daily Air Quality Index summaries from EPA monitors in Keweenaw, Michigan, 1988–2025.

98%

Good days in 2024

Median daily AQI, 2024

Days above 100 in 2024

120

Days with an AQI in 2024 (of 366)

In 2024, EPA reported a daily Air Quality Index (AQI) for Keweenaw, Michigan on 120 days. 118 of those days (98%) were in the Good range, and the median daily AQI was 12. That median is lower than the typical monitored county in Michigan (median 39 across 27 counties), and lower than the typical monitored U.S. county (41). The main pollutant was fine particles (PM2.5) on 120 days. Across the years with fuller monitoring, the share of Good days rose: an average of 94% in 2004–2012 versus 97% in 2017–2024.

EPA did not report an AQI for every day of 2024 here (120 of 366 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

Years with fewer than 120 monitored days (2018, 2019, 2020, 2021, 2023, 2025…) 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.

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 daily AQI
90th-percentile daily AQI

Main pollutant by day, 2024

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.

Pollutant	Days as main pollutant	Share of monitored days
Fine particles (PM2.5)	120	100%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Median AQI	90th pct.	Max AQI	Main pollutant
2025	41	41	0	0	8	16	31	PM2.5
2024	120	118	2	0	12	31	66	PM2.5
2023	119	105	12	2	16	52	141	PM2.5
2022	122	119	3	0	12	32	58	PM2.5
2021	117	109	8	0	14	41	67	PM2.5
2020	117	116	0	1	13	32	124	PM2.5
2019	117	114	3	0	12	28	73	PM2.5
2018	114	108	6	0	12	37	66	PM2.5
2017	121	116	5	0	13	36	64	PM2.5
2016	120	118	2	0	12	33	55	PM2.5
2015	118	111	7	0	17	38	63	PM2.5
2014	115	107	8	0	15	49	65	PM2.5
2013	122	115	7	0	12	37	63	PM2.5
2012	121	115	6	0	15	43	57	PM2.5
2011	121	112	9	0	17	46	88	PM2.5
2010	112	102	10	0	14	46	61	PM2.5
2009	104	95	9	0	14	46	64	PM2.5
2008	118	106	12	0	16	51	95	PM2.5
2007	110	99	11	0	15	51	72	PM2.5
2006	118	105	13	0	16	51	76	PM2.5
2005	119	102	17	0	15	57	73	PM2.5
2004	121	113	8	0	14	43	74	PM2.5
2003	113	102	11	0	17	49	64	PM2.5
2002	114	102	12	0	17	53	65	PM2.5
2001	114	98	16	0	21	54	71	PM2.5
2000	105	98	7	0	18	42	64	PM2.5
1999	9	7	2	0	19	69	69	PM2.5
1991	31	29	2	0	23	38	63	PM2.5
1990	43	38	5	0	24	51	71	PM2.5
1989	57	46	11	0	23	64	72	PM2.5
1988	38	34	4	0	33	55	62	PM2.5

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.

All monitored counties in Michigan

Source: U.S. EPA AirData, “Annual AQI by County” files for 1988–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem