Air Quality in Washington

Washington has 33 counties with EPA air quality monitoring. Air quality is generally improving across the state, with an average of 290 "Good" days per county per year. The best air quality is in Pacific (median AQI 16) and the most polluted is Pierce (median AQI 44).

County	Median AQI	Max AQI	Good Days	Unhealthy Days	Trend	Top Pollutant
Adams	18	71	328	0	→ stable	PM2.5
Asotin	42	196	224	6	↑ worsening	PM2.5
Benton	34	126	299	3	→ stable	PM2.5
Chelan	28	158	293	5	→ stable	PM2.5
Clallam	36	69	321	0	→ stable	Ozone
Clark	31	105	321	1	→ stable	PM2.5
Columbia	36	90	331	0	↑ worsening	Ozone
Cowlitz	22	67	349	0	↓ improving	PM2.5
Franklin	20	75	313	0	→ stable	PM2.5
Garfield	17	85	314	0	↓ improving	PM2.5
Grant	26	84	318	0	→ stable	PM2.5
Grays Harbor	20	64	353	0	↓ improving	PM2.5
Jefferson	21	57	300	0	↓ improving	PM2.5
King	41	119	255	3	→ stable	PM2.5
Kitsap	19	69	341	0	↑ worsening	PM2.5
Kittitas	23	94	320	0	↓ improving	PM2.5
Klickitat	17	64	101	0	↓ improving	PM2.5
Lewis	22	129	336	1	↓ improving	PM2.5
Mason	21	73	341	0	↓ improving	PM2.5
Okanogan	38	102	225	1	→ stable	PM2.5
Pacific	16	54	329	0	↑ worsening	PM2.5
Pend Oreille	26	81	207	0	↑ worsening	PM2.5
Pierce	44	166	265	1	→ stable	Ozone
San Juan	21	52	111	0	↓ improving	PM2.5
Skagit	26	59	357	0	↓ improving	PM2.5
Snohomish	38	99	262	0	→ stable	PM2.5
Spokane	38	106	280	1	→ stable	PM2.5
Stevens	34	98	257	0	→ stable	PM2.5
Thurston	26	85	338	0	↓ improving	PM2.5
Walla Walla	24	87	314	0	→ stable	PM2.5
Whatcom	33	82	335	0	→ stable	PM2.5
Whitman	20	97	310	0	→ stable	PM2.5
Yakima	37	153	248	7	→ stable	PM2.5