San Francisco County, California air quality history

Daily Air Quality Index summaries from EPA monitors in San Francisco, California, 1980–2024.

76%

Good days in 2024

Median daily AQI, 2024

Days above 100 in 2024

334

Days with an AQI in 2024 (of 366)

In 2024, EPA reported a daily Air Quality Index (AQI) for San Francisco, California on 334 days. 254 of those days (76%) were in the Good range, and the median daily AQI was 33. 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 304 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 76% in 1980–1982 versus 76% in 2022–2024.

The most recent year with data for this county is 2024; EPA's files for 2025–2025 contain no row for it, which usually means its monitors stopped reporting.

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)	304	91%
Ozone	22	7%
Nitrogen dioxide (NO₂)	8	2%

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
2024	334	254	80	0	0	0	33	56	94	PM2.5
2023	365	299	65	1	0	0	32	54	117	PM2.5
2022	364	260	104	0	0	0	36	59	88	PM2.5
2021	365	255	110	0	0	0	39	60	86	PM2.5
2020	366	227	131	3	4	1	42	67	223	PM2.5
2019	365	251	113	1	0	0	39	58	108	PM2.5
2018	365	222	129	2	10	2	44	66	252	PM2.5
2017	365	211	147	7	0	0	44	67	136	PM2.5
2016	366	236	130	0	0	0	41	58	71	PM2.5
2015	365	246	119	0	0	0	39	61	100	PM2.5
2014	365	249	116	0	0	0	39	59	97	PM2.5
2013	365	193	170	2	0	0	48	68	133	PM2.5
2012	364	238	124	2	0	0	42	63	105	PM2.5
2011	365	190	173	2	0	0	48	72	131	PM2.5
2010	365	171	191	3	0	0	51	70	125	PM2.5
2009	365	113	247	5	0	0	55	71	136	PM2.5
2008	366	156	208	2	0	0	53	72	110	PM2.5
2007	365	212	148	5	0	0	44	64	125	PM2.5
2006	365	216	145	4	0	0	44	67	147	PM2.5
2005	365	232	126	7	0	0	42	67	122	PM2.5
2004	366	171	188	7	0	0	51	72	149	PM2.5
2003	365	257	103	5	0	0	38	65	116	PM2.5
2002	365	245	99	14	7	0	38	76	161	PM2.5
2001	365	249	103	10	3	0	38	66	166	PM2.5
2000	366	245	115	6	0	0	38	70	132	PM2.5
1999	365	266	83	14	2	0	38	73	162	NO2
1998	365	354	11	0	0	0	33	43	79	NO2
1997	365	340	25	0	0	0	32	45	64	NO2
1996	366	337	29	0	0	0	35	48	80	NO2
1995	365	333	32	0	0	0	34	49	90	NO2
1994	365	322	43	0	0	0	33	51	90	NO2
1993	365	316	49	0	0	0	37	57	79	NO2
1992	366	333	33	0	0	0	33	47	89	NO2
1991	365	293	72	0	0	0	38	57	100	NO2
1990	365	308	53	4	0	0	32	57	106	NO2
1989	365	283	79	3	0	0	38	68	108	NO2
1988	366	283	78	4	1	0	38	70	156	NO2
1987	365	298	63	4	0	0	38	67	110	CO
1986	365	265	96	3	1	0	39	68	153	NO2
1985	365	261	97	6	1	0	45	69	193	NO2
1984	366	256	102	8	0	0	45	79	123	NO2
1983	365	269	89	7	0	0	41	68	108	NO2
1982	365	271	87	6	1	0	39	68	185	NO2
1981	365	282	80	3	0	0	38	68	103	NO2
1980	366	280	73	13	0	0	38	79	127	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 1980–2024 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem