Bad Air Days in Tehama County, California: 16 a Year

16 bad air days a year

Among the worst tenth of monitored US counties. Ranked 43 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (50% particle days).

Which months to watch

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

What actually helps 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.
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.

The worst days on file

In 2000 to 2009 this county averaged 43 bad days a year; in 2016 to 2025, 16. The air has improved. The worst recent year was 2016, with 42 bad days on 366 monitored days.

Date	AQI	Main pollutant
2020-09-13	218	PM2.5
2020-09-14	213	PM2.5
2018-11-15	206	PM2.5
2021-08-31	193	PM2.5
2020-08-22	192	PM2.5

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in Tehama County rated Good on 65% of them, less often than the 72% typical of monitored counties, and Moderate on 31%. The median day sat at AQI 44; one day in ten went above 81.

The pollutant setting the AQI on an ordinary day here:

ozone71%2,604 days
fine particles (PM2.5)28%1,038 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	284	80	1	0	38	108
2024	366	252	112	2	0	43	109
2023	365	242	117	6	0	44	136
2022	365	245	117	3	0	44	108
2021	365	207	122	36	15	47	193
2020	366	216	117	33	21	46	218
2019	365	263	102	0	0	43	93
2018	365	208	128	29	13	48	206
2017	365	237	119	9	3	42	172
2016	366	218	106	42	5	45	174
2015	365	223	123	19	1	47	154
2014	364	227	121	16	1	45	151
2013	365	233	121	11	0	44	136
2012	366	183	164	19	0	51	150
2011	365	133	217	15	0	55	122
2010	365	128	219	18	0	55	136

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

Nearby counties on file

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.