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Air quality in Washington

EPA monitors report from 32 of Washington’s 39 counties. That is the honest limit of this page: the other 7 are not measured, not clean. In 2025 the most affected monitored county was Chelan County, with 14 days above the moderate category.

32
Counties with monitors
7
Counties without
50
Days above moderate, 2025
Summed across monitored counties
10.7%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Washington counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2025 days by category
Chelan County6814233
Stevens County639243
Okanogan County674160
Asotin County673151
Grant County593154
Kittitas County573114
Spokane County633126
Yakima County683154
Benton County572113
Franklin County522109
Klickitat County531119
Mason County481159
Snohomish County611125
Whatcom County461152
Adams County50099
Clallam County53069
Clark County56083
Columbia County50094
Cowlitz County49072
Garfield County45097
Grays Harbor County41076
Jefferson County36059
King County61097
Kitsap County42061
Lewis County48074
Pacific County26051
Pend Oreille County52081
Pierce County580100
Skagit County40057
Thurston County47065
Walla Walla County56085
Whitman County54099

EPA Air Quality System annual summaries by county, 2025. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.

Not measured

7 counties without a monitor

No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.

Other states

Air quality elsewhere