Bad Air Days in Humboldt County, California: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 389 of 996 monitored counties, where 1 is worst.

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

When the bad days come in Humboldt

Most bad days here fall in August and September. 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.

Better or worse than it was

In 2000 to 2009 this county averaged under 1 bad days a year; in 2016 to 2025, 3. It has got worse. The worst recent year was 2023, with 11 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-08-19	299	PM2.5
2023-08-20	253	PM2.5
2023-08-18	223	PM2.5
2023-08-21	217	PM2.5
2023-08-17	186	PM2.5

The air on a normal day

Across 3,651 monitored days from 2016 to 2025, the air in Humboldt County rated Good on 84% of them, more often than the 72% typical of monitored counties, and Moderate on 16%. The median day sat at AQI 33; one day in ten went above 54.

The pollutant setting the AQI on an ordinary day here:

ozone56%2,055 days
fine particles (PM2.5)35%1,273 days
coarse dust (PM10)8%302 days

Humboldt County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	285	80	0	0	38	87
2024	366	266	100	0	0	38	86
2023	365	284	70	11	5	32	299
2022	365	340	25	0	0	24	74
2021	365	333	32	0	0	29	64
2020	366	318	44	4	1	29	180
2019	363	340	23	0	0	28	69
2018	365	301	58	6	1	35	167
2017	365	298	59	8	3	37	180
2016	366	288	78	0	0	38	77
2015	365	241	124	0	0	40	91
2014	365	152	207	6	1	53	169
2013	365	226	138	1	0	44	108
2012	366	252	114	0	0	39	76
2011	365	277	88	0	0	38	80
2010	365	348	17	0	0	30	75

*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.