Bad Air Days in Los Angeles County, California: 106 a Year

106 bad air days a year

Among the worst tenth of monitored US counties. Ranked 5 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (13% particle days).

Which months to watch

Most bad days here fall in July and August and June and September. Averaged over 2016 to 2025.

What to buy, and what not to

Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.
Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Sign up for EnviroFlash ozone alerts for this area during the worst months.

The worst days on file

In 2000 to 2009 this county averaged 150 bad days a year; in 2016 to 2025, 106. The air has improved. The worst recent year was 2020, with 137 bad days on 366 monitored days.

Date	AQI	Main pollutant
2021-10-11	281	PM10
2020-07-05	250	PM2.5
2020-09-05	235	Ozone
2024-07-05	230	PM2.5
2016-07-23	226	PM2.5

An ordinary day in Los Angeles

Across 3,653 monitored days from 2016 to 2025, the air in Los Angeles County rated Good on 6% of them, less often than the 72% typical of monitored counties, and Moderate on 64%. The median day sat at AQI 77; one day in ten went above 146.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)49%1,791 days
ozone46%1,666 days
nitrogen dioxide4%142 days
coarse dust (PM10)1%54 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	39	228	98	32	74	201
2024	366	38	195	133	55	80	230
2023	365	41	237	87	35	67	210
2022	365	17	254	94	29	74	209
2021	365	9	259	97	27	79	281
2020	366	35	194	137	60	85	250
2019	365	34	245	86	29	72	201
2018	365	7	250	108	19	78	201
2017	365	9	237	119	46	79	224
2016	366	7	255	104	23	77	226
2015	365	3	230	132	37	80	203
2014	365	8	250	107	28	82	205
2013	365	8	257	100	25	79	197
2012	366	14	222	130	37	84	207
2011	365	2	242	121	39	80	218
2010	365	14	237	114	15	78	200

*2025 may be a partial year in EPA's file.

Elsewhere in California

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, and on why a purifier does not touch ozone in smoke vs ozone.