Bad Air Days in Kern County, California: 109 a Year

109 bad air days a year

Among the worst tenth of monitored US counties. Ranked 3 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (29% particle days).

Which months to watch

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

Is a purifier worth it here?

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.
With this many bad days, whole-home filtration is worth an HVAC contractor quote.
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 Kern

In 2000 to 2009 this county averaged 197 bad days a year; in 2016 to 2025, 109. The air has improved. The worst recent year was 2017, with 139 bad days on 365 monitored days.

Date	AQI	Main pollutant
2019-10-30	553	PM10
2021-10-11	314	PM10
2022-10-22	289	PM10
2020-09-08	267	PM10
2021-09-27	253	PM2.5

An ordinary day in Kern

Across 3,653 monitored days from 2016 to 2025, the air in Kern County rated Good on 17% of them, less often than the 72% typical of monitored counties, and Moderate on 54%. The median day sat at AQI 78; one day in ten went above 134.

The pollutant setting the AQI on an ordinary day here:

ozone56%2,063 days
fine particles (PM2.5)39%1,431 days
coarse dust (PM10)4%157 days

Kern County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	64	236	65	4	70	200
2024	366	76	196	94	21	72	177
2023	365	85	210	70	12	69	174
2022	365	47	196	122	13	80	289
2021	365	35	202	128	31	84	314
2020	366	56	180	130	32	83	267
2019	365	91	179	95	8	69	553
2018	365	45	190	130	27	84	190
2017	365	59	167	139	24	85	197
2016	366	46	204	116	14	80	169
2015	365	23	220	122	29	84	201
2014	365	17	188	160	43	97	307
2013	365	14	215	136	32	90	242
2012	366	39	185	142	50	85	202
2011	365	39	186	140	40	84	200
2010	365	43	197	125	40	81	202

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

California compared

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.