Bad Air Days in Del Norte County, California: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 407 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (100% particle days).

Which months to watch

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

What actually helps here

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

The worst days on file

The worst recent year was 2020, with 9 bad days on 292 monitored days.

Date	AQI	Main pollutant
2017-09-01	251	PM2.5
2020-09-11	245	PM2.5
2020-09-12	203	PM2.5
2017-09-04	200	PM2.5
2020-09-10	198	PM2.5

Most days, not the worst ones

Across 2,831 monitored days from 2016 to 2025, the air in Del Norte County rated Good on 81% of them, more often than the 72% typical of monitored counties, and Moderate on 19%. The median day sat at AQI 31; one day in ten went above 55.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%2,831 days

Del Norte County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	352	288	64	0	0	32	70
2024	289	232	55	2	0	32	125
2023	328	268	52	8	2	32	187
2022	344	299	45	0	0	29	74
2021	323	259	64	0	0	31	72
2020	292	193	90	9	5	42	245
2019	248	210	38	0	0	26	74
2018	180	134	46	0	0	33	80
2017	298	241	55	2	2	27	251
2016	177	156	21	0	0	26	69
2015	114	101	13	0	0	20	72
2014	115	108	7	0	0	16	60
2013	126	121	5	0	0	16	75
2012	119	117	2	0	0	12	54
2011	120	117	3	0	0	17	54
2010	110	109	1	0	0	14	57

*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, on the AQI 100 line in what counts as a bad air day.