Bad Air Days in Jefferson County, Washington: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 576 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. 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

In 2000 to 2009 this county averaged under 1 bad days a year; in 2016 to 2025, 2. Not much has changed. The worst recent year was 2020, with 8 bad days on 340 monitored days.

Date	AQI	Main pollutant
2020-09-14	232	PM2.5
2020-09-12	224	PM2.5
2020-09-13	222	PM2.5
2020-09-15	214	PM2.5
2020-09-11	189	PM2.5

An ordinary day in Jefferson

Across 3,480 monitored days from 2016 to 2025, the air in Jefferson County rated Good on 95% of them, more often than the 72% typical of monitored counties, and Moderate on 5%. The median day sat at AQI 23; one day in ten went above 41.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%3,480 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	335	326	9	0	0	20	59
2024	311	300	11	0	0	21	57
2023	350	336	14	0	0	21	88
2022	349	327	22	0	0	21	90
2021	358	352	6	0	0	20	79
2020	340	321	11	8	6	23	232
2019	365	344	21	0	0	26	57
2018	359	327	26	6	3	25	184
2017	365	328	36	1	0	24	108
2016	348	336	12	0	0	24	65
2015	307	275	32	0	0	26	75
2014	342	302	40	0	0	27	68
2013	362	320	42	0	0	28	68
2012	347	333	14	0	0	24	63
2011	363	331	32	0	0	25	65
2010	355	329	26	0	0	24	66

*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.