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California Air Quality

EPA monitor data through 2025 · Updated August 13, 2026 · Methods

In 2025, California recorded 195 days above an Air Quality Index of 100, the level at which EPA begins warning sensitive groups, out of 365 days with monitoring data. Most of those bad days were driven by ozone. Under the AQI rules that applied before 2013, the same air would have scored 147 days. Since 2000, unhealthy days are 47% lower on a consistent definition.

Unhealthy days, 2025

195

AQI above 100

Same air, pre-2013 rules

147

for comparison with older reports

Good-air days

AQI 50 or below

Days monitored

365

full year

How to read a statewide figure. The Air Quality Index describes one place at one time. A statewide number is the worst monitor anywhere in the state on each day, so it answers “was the air unhealthy somewhere in California?” — not “what did a typical resident breathe?” In a large state with many monitors it will read high even if most of the state was clean. EPA publishes the AQI for metropolitan areas rather than states for exactly this reason. For what people actually breathed, use the metro pages below.

Unhealthy days by year, scored two ways

EPA changed what an AQI of 100 means in 2013 and again in 2015, so a count published before those changes is not comparable to one published after. Each panel below applies a single fixed rulebook to every year, so each is internally consistent. Why this matters.

Scored by today's rules

Scored by the pre-2013 rules

What 2025 looked like

Air quality category	Days	Share of monitored days
Good	1	0%
Moderate	169	46%
Unhealthy for sensitive groups	117	32%
Unhealthy or worse	78	21%

Median AQI 102 · 90th-percentile AQI 169 · worst day 6180. Scored under current rules.

What drove the unhealthy days

Of the 195 days above 100 in 2025, 114 were driven by ozone and 54 by fine particles, with 27 from another pollutant. The two behave differently. Ozone peaks on hot sunny afternoons; fine particles now spike mainly with wildfire smoke. In the western United States, ozone is a different problem: the floor is rising, with even the cleanest summer days at high elevation now near 40 ppb, and bad years track wildfire seasons. Domestic emission cuts have less room to work against that.

The unhealthy days in 2025

Every day the index passed 100, what it reached, and which pollutant drove it. 48 of these 195 would not have counted as unhealthy under the pre-2013 rules.

Date	Peak AQI	Driven by	Pre-2013 score
Jan 1	166	Fine particles	157
Jan 2	132	Fine particles	116
Jan 3	101	Fine particles	91 (not unhealthy)
Jan 4	136	Fine particles	119
Jan 7	365	Coarse particles	374
Jan 8	426	Coarse particles	433
Jan 9	164	Fine particles	156
Jan 10	163	Fine particles	155
Jan 17	111	Fine particles	98 (not unhealthy)
Jan 18	109	Fine particles	97 (not unhealthy)
Jan 19	103	Fine particles	92 (not unhealthy)
Jan 20	115	Coarse particles	115
Jan 22	125	Fine particles	110
Jan 23	105	Fine particles	93 (not unhealthy)
Jan 24	102	Fine particles	91 (not unhealthy)
Jan 25	135	Fine particles	119
Jan 30	110	Fine particles	97 (not unhealthy)
Jan 31	107	Fine particles	95 (not unhealthy)
Feb 1	112	Fine particles	99 (not unhealthy)
Feb 2	109	Fine particles	97 (not unhealthy)
Feb 11	185	Coarse particles	185
Mar 1	174	Coarse particles	174
Mar 2	112	Coarse particles	112
Mar 6	142	Coarse particles	142
Mar 12	115	Coarse particles	115
Mar 22	101	Ozone	87 (not unhealthy)
Mar 26	120	Coarse particles	120
Mar 27	127	Coarse particles	127
Mar 30	114	Coarse particles	114
Apr 1	171	Coarse particles	171
Apr 8	122	Ozone	104
Apr 9	136	Ozone	114
Apr 10	154	Ozone	129
Apr 11	143	Ozone	119
Apr 16	709	Coarse particles	688
Apr 17	112	Coarse particles	112
Apr 18	136	Coarse particles	136
Apr 20	101	Ozone	87 (not unhealthy)
Apr 21	101	Ozone	87 (not unhealthy)
Apr 22	101	Ozone	87 (not unhealthy)
Apr 25	188	Coarse particles	188
May 2	101	Ozone	87 (not unhealthy)
May 4	116	Coarse particles	116
May 8	129	Ozone	109
May 9	154	Ozone	129
May 10	159	Ozone	135
May 11	136	Ozone	114
May 13	187	Coarse particles	187
May 17	190	Coarse particles	190
May 19	108	Ozone	93 (not unhealthy)
May 20	156	Ozone	132
May 21	169	Ozone	145
May 22	166	Ozone	142
May 23	126	Ozone	106
May 25	101	Ozone	87 (not unhealthy)
May 26	105	Ozone	90 (not unhealthy)
May 27	133	Ozone	111
May 28	122	Ozone	104
May 29	156	Ozone	132
May 30	159	Ozone	135
May 31	164	Ozone	140
Jun 1	112	Ozone	97 (not unhealthy)
Jun 4	108	Ozone	93 (not unhealthy)
Jun 5	105	Ozone	90 (not unhealthy)
Jun 6	140	Ozone	116
Jun 7	143	Ozone	119
Jun 8	133	Ozone	111
Jun 9	154	Ozone	129
Jun 10	187	Ozone	161
Jun 11	179	Ozone	154
Jun 12	150	Ozone	124
Jun 13	182	Ozone	156
Jun 14	164	Ozone	140
Jun 15	174	Ozone	150
Jun 16	195	Ozone	169
Jun 17	207	Ozone	192
Jun 18	205	Ozone	187
Jun 19	166	Ozone	142
Jun 20	122	Ozone	104
Jun 21	183	Coarse particles	183
Jun 25	156	Ozone	132
Jun 26	169	Ozone	145
Jun 27	151	Ozone	127
Jun 28	159	Ozone	135
Jun 29	129	Ozone	109
Jun 30	105	Ozone	90 (not unhealthy)
Jul 1	161	Ozone	137
Jul 2	150	Ozone	124
Jul 3	136	Ozone	114
Jul 4	151	Fine particles	132
Jul 5	170	Fine particles	161
Jul 6	150	Ozone	124
Jul 7	169	Ozone	145
Jul 8	166	Ozone	142
Jul 9	172	Ozone	147
Jul 10	201	Ozone	177
Jul 11	169	Ozone	145
Jul 12	150	Ozone	124
Jul 13	154	Fine particles	140
Jul 14	182	Ozone	156
Jul 15	133	Ozone	111
Jul 16	112	Ozone	97 (not unhealthy)
Jul 17	108	Ozone	93 (not unhealthy)
Jul 18	133	Ozone	111
Jul 19	136	Ozone	114
Jul 20	112	Ozone	97 (not unhealthy)
Jul 22	101	Ozone	87 (not unhealthy)
Jul 23	101	Ozone	87 (not unhealthy)
Jul 27	119	Ozone	101
Jul 28	136	Ozone	114
Jul 29	147	Ozone	122
Jul 30	133	Ozone	111
Jul 31	136	Ozone	114
Aug 1	119	Ozone	101
Aug 2	143	Ozone	119
Aug 3	161	Ozone	137
Aug 4	166	Ozone	142
Aug 5	156	Ozone	132
Aug 6	190	Ozone	164
Aug 7	161	Ozone	137
Aug 8	156	Ozone	132
Aug 9	166	Ozone	142
Aug 10	140	Ozone	116
Aug 11	187	Ozone	161
Aug 12	192	Ozone	166
Aug 13	166	Ozone	142
Aug 14	156	Ozone	132
Aug 15	140	Ozone	116
Aug 18	150	Ozone	124
Aug 19	161	Ozone	137
Aug 20	182	Ozone	156
Aug 21	202	Ozone	179
Aug 22	187	Ozone	161
Aug 23	126	Ozone	106
Aug 24	2035	Coarse particles	1881
Aug 25	6180	Coarse particles	5609
Aug 26	122	Ozone	104
Aug 28	113	Coarse particles	113
Aug 29	151	Ozone	127
Aug 30	177	Ozone	151
Aug 31	166	Fine particles	158
Sep 1	150	Fine particles	130
Sep 2	119	Ozone	101
Sep 3	166	Ozone	142
Sep 4	147	Ozone	129
Sep 5	101	Ozone	87 (not unhealthy)
Sep 6	145	Fine particles	126
Sep 7	265	Fine particles	240
Sep 8	704	Fine particles	659
Sep 9	229	Fine particles	204
Sep 10	117	Fine particles	104
Sep 14	133	Ozone	111
Sep 15	182	Ozone	156
Sep 16	122	Ozone	104
Sep 17	136	Ozone	114
Sep 20	108	Ozone	93 (not unhealthy)
Sep 21	112	Ozone	97 (not unhealthy)
Sep 23	140	Ozone	116
Sep 27	108	Ozone	93 (not unhealthy)
Oct 13	181	Coarse particles	181
Oct 17	107	Fine particles	95 (not unhealthy)
Oct 18	103	Fine particles	92 (not unhealthy)
Oct 19	119	Ozone	101
Oct 21	119	Ozone	101
Oct 22	164	Fine particles	156
Oct 31	102	Nitrogen dioxide	102
Nov 1	115	Ozone	100 (not unhealthy)
Nov 2	108	Fine particles	96 (not unhealthy)
Nov 3	105	Fine particles	94 (not unhealthy)
Nov 5	154	Coarse particles	154
Nov 12	105	Fine particles	94 (not unhealthy)
Nov 13	200	Coarse particles	200
Nov 21	123	Fine particles	109
Nov 24	101	Fine particles	91 (not unhealthy)
Nov 26	106	Fine particles	95 (not unhealthy)
Nov 27	114	Fine particles	102
Nov 30	109	Fine particles	96 (not unhealthy)
Dec 6	120	Fine particles	107
Dec 7	102	Fine particles	91 (not unhealthy)
Dec 8	112	Fine particles	99 (not unhealthy)
Dec 9	117	Fine particles	104
Dec 12	107	Fine particles	95 (not unhealthy)
Dec 13	151	Fine particles	132
Dec 14	162	Fine particles	155
Dec 15	137	Fine particles	120
Dec 16	118	Fine particles	105
Dec 17	152	Fine particles	134
Dec 18	141	Fine particles	123
Dec 19	109	Fine particles	97 (not unhealthy)
Dec 20	109	Fine particles	97 (not unhealthy)
Dec 21	107	Fine particles	95 (not unhealthy)
Dec 22	105	Fine particles	93 (not unhealthy)
Dec 23	103	Fine particles	92 (not unhealthy)
Dec 24	126	Ozone	106
Dec 25	129	Ozone	109

Metro areas in California

Ranked by unhealthy days in their latest year. These are the geographies EPA actually reports the AQI for.

Metro area	Unhealthy days	Pre-2013 rules	Main driver
Riverside-San Bernardino-Ontario, CA	136	108	ozone
Los Angeles-Long Beach-Anaheim, CA	99	71	ozone
Bakersfield, CA	63	28	ozone
El Centro, CA	45	32	ozone
Visalia-Porterville, CA	43	15	ozone
Fresno, CA	34	18	ozone
San Diego-Carlsbad, CA	32	14	ozone
Bishop, CA	13	7	ozone
Hanford-Corcoran, CA	11	1	ozone
Oxnard-Thousand Oaks-Ventura, CA	8	4	ozone
San Luis Obispo-Paso Robles-Arroyo Grande, CA	7	1	ozone
Sacramento--Roseville--Arden-Arcade, CA	5	4	ozone
Madera, CA	3	1	ozone
Modesto, CA	3	0	ozone
Red Bluff, CA	1	0	ozone
Redding, CA	1	1	fine particles
Sonora, CA	1	0	ozone
Truckee-Grass Valley, CA	1	0	ozone
Chico, CA	0	0	ozone and fine particles equally
Clearlake, CA	0	0	ozone and fine particles equally
Eureka-Arcata-Fortuna, CA	0	0	ozone and fine particles equally
Merced, CA	0	0	ozone and fine particles equally
Napa, CA	0	0	ozone and fine particles equally
Salinas, CA	0	0	ozone and fine particles equally
San Francisco-Oakland-Hayward, CA	0	0	ozone and fine particles equally
San Jose-Sunnyvale-Santa Clara, CA	0	0	ozone and fine particles equally
Santa Cruz-Watsonville, CA	0	0	ozone and fine particles equally
Santa Maria-Santa Barbara, CA	0	0	ozone and fine particles equally
Santa Rosa, CA	0	0	ozone and fine particles equally
Stockton-Lodi, CA	0	0	ozone and fine particles equally
Ukiah, CA	0	0	ozone and fine particles equally
Vallejo-Fairfield, CA	0	0	ozone and fine particles equally
Yuba City, CA	0	0	ozone and fine particles equally

The full series

Year	Unhealthy days, current rules	Pre-2013 rules	Days monitored
2000	291	275	366
2001	323	310	365
2002	319	303	365
2003	302	280	365
2004	300	269	366
2005	259	237	365
2006	264	239	365
2007	297	272	365
2008	274	251	366
2009	261	230	365
2010	236	210	365
2011	271	240	365
2012	274	236	366
2013	265	228	365
2014	276	235	365
2015	256	218	365
2016	254	216	366
2017	269	236	365
2018	241	198	365
2019	214	172	365
2020	248	220	366
2021	259	227	365
2022	271	234	365
2023	216	182	365
2024	210	182	366
2025	195	147	365

Sources

EPA AirData daily monitor files, recomputed under both breakpoint tables. Methods and validation.
Download the full dataset for every state and metro.