Marin County, California air quality history

Daily Air Quality Index summaries from EPA monitors in Marin, California, 1980–2025.

86%

Good days in 2024

Median daily AQI, 2024

Days above 100 in 2024

357

Days with an AQI in 2024 (of 366)

In 2024, EPA reported a daily Air Quality Index (AQI) for Marin, California on 357 days. 308 of those days (86%) were in the Good range, and the median daily AQI was 28. That median is lower than the typical monitored county in California (median 46.5 across 52 counties), and lower than the typical monitored U.S. county (41). The main pollutant was fine particles (PM2.5) on 307 days. Across the years with fuller monitoring, the share of Good days fell: an average of 86% in 1980–1982 versus 83% in 2022–2024.

Years with fewer than 120 monitored days (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)	307	86%
Ozone	47	13%
Nitrogen dioxide (NO₂)	3	1%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Very Unhealthy	Median AQI	90th pct.	Max AQI	Main pollutant
2025	95	87	8	0	0	0	21	49	66	PM2.5
2024	357	308	49	0	0	0	28	52	86	PM2.5
2023	363	315	48	0	0	0	34	52	99	Ozone
2022	365	275	90	0	0	0	37	57	91	PM2.5
2021	365	267	98	0	0	0	38	60	88	PM2.5
2020	366	272	85	4	4	1	36	62	231	PM2.5
2019	363	291	71	1	0	0	37	55	133	PM2.5
2018	365	235	117	3	9	1	43	63	243	PM2.5
2017	365	224	133	5	3	0	44	62	164	PM2.5
2016	366	296	70	0	0	0	36	55	90	PM2.5
2015	365	226	137	2	0	0	43	64	103	PM2.5
2014	365	130	234	1	0	0	53	65	107	PM2.5
2013	365	157	206	2	0	0	52	66	124	PM2.5
2012	366	254	112	0	0	0	42	58	83	PM2.5
2011	365	183	181	1	0	0	50	64	117	PM2.5
2010	365	191	170	4	0	0	49	63	128	PM2.5
2009	365	316	49	0	0	0	32	55	98	Ozone
2008	366	339	27	0	0	0	31	47	97	Ozone
2007	365	349	16	0	0	0	30	42	81	Ozone
2006	365	346	19	0	0	0	31	43	68	Ozone
2005	365	350	15	0	0	0	29	42	65	Ozone
2004	363	345	18	0	0	0	29	41	80	NO2
2003	365	345	20	0	0	0	28	43	90	NO2
2002	365	332	33	0	0	0	30	48	85	NO2
2001	365	339	26	0	0	0	30	46	84	NO2
2000	366	353	13	0	0	0	28	42	61	NO2
1999	365	326	38	1	0	0	32	52	133	NO2
1998	365	350	15	0	0	0	30	42	69	NO2
1997	365	341	23	1	0	0	29	44	108	Ozone
1996	366	330	35	1	0	0	31	50	136	NO2
1995	365	342	22	1	0	0	30	45	105	NO2
1994	365	322	43	0	0	0	32	52	86	NO2
1993	365	318	47	0	0	0	33	52	86	NO2
1992	366	335	31	0	0	0	34	47	80	NO2
1991	365	307	58	0	0	0	38	57	93	NO2
1990	365	312	53	0	0	0	34	55	81	NO2
1989	365	298	67	0	0	0	38	57	100	Ozone
1988	365	327	37	1	0	0	28	51	119	Ozone
1987	362	324	36	2	0	0	38	51	119	NO2
1986	365	309	54	2	0	0	38	57	103	NO2
1985	365	329	35	1	0	0	38	50	122	NO2
1984	366	316	43	7	0	0	38	57	143	NO2
1983	365	336	28	0	1	0	38	47	164	NO2
1982	365	326	38	1	0	0	38	57	103	NO2
1981	365	329	34	2	0	0	38	50	112	NO2
1980	366	284	70	12	0	0	38	68	115	NO2

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.

Counties in California with a similar median AQI in 2024

All monitored counties in California

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem