Bad Air Days in Lake County, California: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 679 of 996 monitored counties, where 1 is worst.

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

The bad-air season here

Most bad days here fall in August and September and November. 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 record for Lake

In 2000 to 2009 this county averaged 1 bad days a year; in 2016 to 2025, 1. Not much has changed. The worst recent year was 2020, with 4 bad days on 351 monitored days.

Date	AQI	Main pollutant
2018-11-10	233	PM2.5
2020-08-25	190	PM2.5
2017-10-10	172	PM2.5
2020-09-30	172	PM2.5
2018-08-08	162	PM2.5

An ordinary day in Lake

Across 3,603 monitored days from 2016 to 2025, the air in Lake County rated Good on 98% of them, more often than the 72% typical of monitored counties, and Moderate on 2%. The median day sat at AQI 32; one day in ten went above 42.

The pollutant setting the AQI on an ordinary day here:

ozone96%3,474 days
fine particles (PM2.5)3%121 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	363	360	3	0	0	31	74
2024	363	361	2	0	0	32	67
2023	363	357	6	0	0	32	67
2022	363	359	4	0	0	32	76
2021	356	348	7	1	1	33	157
2020	351	341	6	4	3	32	190
2019	360	360	0	0	0	31	50
2018	357	344	10	3	2	33	233
2017	362	350	10	2	1	35	172
2016	365	356	9	0	0	33	74
2015	363	351	11	1	0	36	148
2014	357	333	24	0	0	37	93
2013	364	355	9	0	0	33	80
2012	362	336	23	3	0	35	143
2011	365	359	6	0	0	34	54
2010	361	356	5	0	0	35	74

*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.