Bad Air Days in Ventura County, California: 15 a Year

15 bad air days a year

Among the worst tenth of monitored US counties. Ranked 49 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (19% particle days).

The bad-air season here

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

What actually helps here

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 record for Ventura

In 2000 to 2009 this county averaged 66 bad days a year; in 2016 to 2025, 15. The air has improved. The worst recent year was 2017, with 33 bad days on 365 monitored days.

Date	AQI	Main pollutant
2017-12-06	961	PM2.5
2017-12-08	906	PM2.5
2017-12-07	261	PM2.5
2017-12-09	254	PM2.5
2017-12-12	250	PM2.5

The air on a normal day

Across 3,653 monitored days from 2016 to 2025, the air in Ventura County rated Good on 44% of them, less often than the 72% typical of monitored counties, and Moderate on 52%. The median day sat at AQI 52; one day in ten went above 83.

The pollutant setting the AQI on an ordinary day here:

ozone56%2,039 days
fine particles (PM2.5)42%1,546 days
coarse dust (PM10)2%64 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	190	167	8	0	50	131
2024	366	191	160	15	1	50	176
2023	365	220	133	12	0	46	136
2022	365	171	183	11	0	52	140
2021	365	157	198	10	0	53	122
2020	366	185	155	26	5	50	174
2019	365	175	181	9	0	51	126
2018	365	94	254	17	1	57	166
2017	365	117	215	33	13	57	961
2016	366	120	237	9	0	56	147
2015	365	119	233	13	0	56	126
2014	365	101	249	15	0	58	150
2013	365	116	238	11	1	55	159
2012	366	116	218	32	1	58	154
2011	365	208	141	16	2	48	151
2010	365	202	145	18	4	48	161

*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, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.