Air Quality Rankings for California 2026

California has 53 cities with EPA air quality data. Humboldt, California has the cleanest air with a 5-year average AQI of 28. San Bernardino, California has the highest AQI at 82.

#	City	5yr Avg AQI	Current AQI	Worst Pollutant	Trend	Grade
1	Humboldt, California	28	32	Ozone	Improving	A
2	Del Norte, California	32	32	PM2.5	Worsening	C
3	Lake, California	32	32	Ozone	Improving	B
4	Trinity, California	32	31	PM2.5	Worsening	C
5	Mono, California	33	24	PM2.5	Worsening	D
6	Sonoma, California	36	33	Ozone	Improving	B
7	San Mateo, California	36	31	PM2.5	Improving	B
8	Marin, California	36	34	PM2.5	Improving	B
9	Amador, California	37	36	Ozone	Improving	B
10	Santa Cruz, California	37	36	PM2.5	Stable	B
11	San Francisco, California	38	32	PM2.5	Improving	B
12	Napa, California	39	41	PM2.5	Improving	B
13	Monterey, California	40	42	Ozone	Stable	C
14	San Benito, California	41	40	Ozone	Stable	C
15	Siskiyou, California	41	43	Ozone	Worsening	D
16	Tuolumne, California	41	43	Ozone	Improving	B
17	Glenn, California	43	41	Ozone	Improving	C
18	Yolo, California	43	43	Ozone	Improving	B
19	El Dorado, California	43	44	Ozone	Stable	C
20	Calaveras, California	44	40	Ozone	Improving	B
21	Shasta, California	44	45	Ozone	Stable	C
22	Solano, California	45	40	PM2.5	Improving	B
23	Tehama, California	45	44	Ozone	Stable	C
24	Mendocino, California	46	53	PM2.5	Worsening	C
25	Santa Barbara, California	46	45	PM2.5	Improving	B
26	Nevada, California	47	42	Ozone	Stable	C
27	Colusa, California	47	55	PM2.5	Stable	C
28	Contra Costa, California	48	51	PM2.5	Stable	C
29	Mariposa, California	49	47	Ozone	Improving	C
30	Santa Clara, California	49	43	PM2.5	Stable	C
31	San Joaquin, California	50	47	PM2.5	Improving	C
32	Alameda, California	50	48	PM2.5	Improving	C
33	Ventura, California	50	46	PM2.5	Improving	C
34	San Luis Obispo, California	51	47	PM2.5	Improving	C
35	Butte, California	52	50	PM2.5	Improving	C
36	Sutter, California	52	49	PM2.5	Improving	C
37	Plumas, California	52	50	PM2.5	Worsening	D
38	Sacramento, California	53	51	Ozone	Improving	C
39	Merced, California	54	51	Ozone	Improving	C
40	Orange, California	54	52	PM2.5	Improving	C
41	Placer, California	54	52	Ozone	Worsening	D
42	Madera, California	56	52	Ozone	Improving	C
43	Inyo, California	57	61	Ozone	Worsening	F
44	Stanislaus, California	57	54	PM2.5	Improving	D
45	Imperial, California	61	61	PM2.5	Improving	D
46	Kings, California	64	58	Ozone	Improving	D
47	San Diego, California	67	67	PM2.5	Stable	D
48	Fresno, California	68	64	Ozone	Improving	D
49	Tulare, California	75	69	Ozone	Improving	D
50	Los Angeles, California	75	67	PM2.5	Improving	D
51	Kern, California	77	69	Ozone	Improving	D
52	Riverside, California	82	79	Ozone	Improving	D
53	San Bernardino, California	82	71	Ozone	Improving	F

Air quality data for California is sourced from the EPA Air Quality System (AQS), which monitors outdoor air quality at thousands of stations nationwide.
— EPA Air Quality System

Frequently Asked Questions

Humboldt, California has the best air quality in California with a 5-year average AQI of 28 and a grade of A.

California has 53 cities with EPA air quality monitoring data in our database, covering multiple years of AQI measurements.

The Air Quality Index (AQI) measures five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Lower AQI values indicate cleaner air — 0-50 is "Good," while 150+ is "Unhealthy."

Sources: EPA Air Quality System (AQS)

Cities ranked by 5-year average AQI (lower is better). Grades factor in average AQI, trend direction, unhealthy days, and dominant pollutant.

Cleanest Cities Nationwide →All Air Quality in California →