This is because a temperature inversion is limiting downward mixing. Here's the 5PM temperature sounding from Quillayute on Saturday, showing the inversion:
Models persist with this 3000- 5000 ft inversion through Tuesday, and if that prediction holds, it should keep most of the smoke above. Other models however mix some smoke to surface during the daytime hours on Sunday and Monday, so uncertainty persists. Air could range from Good to Unhealthy for Sensitive Groups in western WA, with both smoke and smog contributing- more on smog later.
Eastern WA doesnt have such a temperature inversion to keep the smoke aloft, so as long as the northerly flow persists, BC smoke will continue to mix downward. Air quality is not expected to improve a whole lot all week. Although a few Moderate areas might appear occasionally, folks need to be prepared for a repeat of the above map. Air will remain Unhealthy for Sensitive Groups, if not worse.
A pattern shift that will help us ventilate out isn't on the cards until Saturday. The 10K ft winds advertised by the European model only turn southwest for the first time in over a week on Saturday morning.
Wildfires are copious sources of one of the precursor gases and many ozone monitors in WA recorded high levels of ozone over the last few days.
Even when wildfire smoke is taken out of the equation, Washington state continues to have ozone concerns in the Cascade foothills of east King/ Pierce county, and in the Tri-Cities. Several air quality agencies are working with stakeholders to protect the public from this health risk.