Bad Air Days in Siskiyou County, California: 14 a Year

14 bad air days a year

Among the worst tenth of monitored US counties. Ranked 56 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (99% particle days).

When the bad days come in Siskiyou

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.

The record for Siskiyou

In 2000 to 2009 this county averaged 1 bad days a year; in 2016 to 2025, 14. It has got worse. The worst recent year was 2018, with 40 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-09-12	468	PM2.5
2022-07-31	454	PM2.5
2023-08-28	320	PM2.5
2020-09-13	319	PM2.5
2023-09-23	263	PM2.5

Most days, not the worst ones

Across 3,503 monitored days from 2016 to 2025, the air in Siskiyou County rated Good on 78% of them, more often than the 72% typical of monitored counties, and Moderate on 19%. The median day sat at AQI 38; one day in ten went above 67.

The pollutant setting the AQI on an ordinary day here:

ozone61%2,132 days
fine particles (PM2.5)39%1,371 days

Siskiyou County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	363	284	75	4	2	37	166
2024	366	294	72	0	0	40	94
2023	365	270	78	17	10	43	320
2022	362	269	86	7	5	41	454
2021	364	237	96	31	24	43	210
2020	366	272	71	23	13	39	468
2019	365	302	59	4	2	38	164
2018	365	247	78	40	24	42	219
2017	225	198	23	4	1	28	167
2016	362	351	11	0	0	27	93
2015	362	330	28	4	0	36	139
2014	363	330	31	2	2	37	162
2013	361	323	34	4	0	37	121
2012	362	324	35	3	2	37	168
2011	356	334	22	0	0	37	71
2010	361	350	11	0	0	33	90

*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.