Sonoma County, California air quality history

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

100%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

365

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Sonoma, California on 365 days. 365 of those days (100%) were in the Good range, and the median daily AQI was 9. That median is lower than the typical monitored county in California (median 45.5 across 46 counties), and lower than the typical monitored U.S. county (40). The main pollutant was coarse particles (PM10) on 365 days. Across the years with fuller monitoring, the share of Good days rose: an average of 87% in 1980–1982 versus 95% in 2023–2025.

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, 2025

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
Coarse particles (PM10)	365	100%

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	365	365	0	0	0	0	9	17	39	PM10
2024	366	348	18	0	0	0	19	41	72	PM2.5
2023	365	323	40	2	0	0	33	51	117	Ozone
2022	365	286	79	0	0	0	36	56	82	Ozone
2021	365	283	82	0	0	0	37	57	89	PM2.5
2020	366	290	69	1	6	0	36	57	199	PM2.5
2019	365	318	47	0	0	0	36	52	87	Ozone
2018	365	304	48	3	8	2	39	57	250	Ozone
2017	365	267	93	2	3	0	41	60	169	Ozone
2016	366	323	43	0	0	0	34	51	87	Ozone
2015	365	293	72	0	0	0	37	58	90	Ozone
2014	365	257	108	0	0	0	42	58	83	PM2.5
2013	365	240	125	0	0	0	41	65	86	PM2.5
2012	366	240	126	0	0	0	41	61	82	PM2.5
2011	365	225	140	0	0	0	40	64	96	PM2.5
2010	365	268	97	0	0	0	36	59	93	PM2.5
2009	365	300	65	0	0	0	33	59	88	Ozone
2008	366	322	44	0	0	0	37	52	91	Ozone
2007	365	326	39	0	0	0	35	52	94	Ozone
2006	365	325	39	0	1	0	34	52	153	Ozone
2005	365	338	27	0	0	0	32	46	97	Ozone
2004	366	328	37	1	0	0	33	51	122	Ozone
2003	365	318	45	2	0	0	37	54	133	Ozone
2002	365	305	55	5	0	0	37	59	138	Ozone
2001	365	307	52	5	1	0	37	58	165	Ozone
2000	366	311	48	7	0	0	37	56	122	Ozone
1999	365	293	60	10	2	0	38	63	154	Ozone
1998	361	321	29	6	4	1	37	51	201	Ozone
1997	365	324	32	8	1	0	35	54	164	Ozone
1996	366	335	28	3	0	0	37	49	122	Ozone
1995	365	337	23	4	1	0	37	47	161	Ozone
1994	365	342	20	3	0	0	37	47	133	Ozone
1993	365	333	29	3	0	0	37	48	108	Ozone
1992	366	330	34	2	0	0	37	50	133	Ozone
1991	365	322	39	4	0	0	37	55	126	Ozone
1990	365	326	38	1	0	0	35	51	108	Ozone
1989	365	313	43	9	0	0	35	57	143	Ozone
1988	364	321	35	7	1	0	37	51	177	Ozone
1987	363	310	44	7	2	0	37	58	179	Ozone
1986	365	326	37	2	0	0	33	51	126	Ozone
1985	365	317	42	4	2	0	37	58	164	Ozone
1984	366	320	36	8	2	0	35	57	154	NO2
1983	365	334	30	0	1	0	30	47	156	NO2
1982	365	334	29	2	0	0	35	48	101	Ozone
1981	365	328	37	0	0	0	38	51	89	Ozone
1980	366	295	61	5	5	0	38	68	174	Ozone

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 2025

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