Monday, August 7, 2017

Monday and Tuesday will be like Sunday

For smoke that is, not because of an extended weekend.

The Canadian smoke model had it right yesterday- the inversion over western WA did break in the afternoon, mixing smoke to the Puget Sound lowlands. As winds died down, more smoke built up over the area. Sunset was more colorful than Friday and Saturday. Air was Moderate in most of western WA and Unhealthy for Sensitive Groups (USG) or worse in most of eastern WA.

The stark air quality divide across the Cascades persists. The air quality animation of the last few hours shows how areas west of the Cascades have improved compared to eastern WA, eastern OR and south central ID - which still have the ignoble distinction of having the worst air in the country.

Because it has been doing a reasonable job over the last few days, will lean on the Canadian model for guidance. Expecting a repeat of yesterday for both Monday and Tuesday: western WA mostly Moderate, eastern WA mostly USG; Very Unhealthy in areas closer to local fires.

The issue of large differences in pollution levels within a short distance has been raised. It seems reasonable that when smoke from a common source blankets a large area, concentrations should be fairly uniform. If large differences are observed, is it due to malfunctioning monitors?

Malfunctioning equipment is a concern and site operators work hard to ensure accurate and timely data delivery. However even in absence of localized sources, concentration gradients can arise due to differences in topography. Below is a comparison of two pairs of sites within ~15 miles of each other, showing very different levels this morning. The site at Neah Bay is at sea level and the site at Cheeka Peak is about 15 miles south and 1000ft above (difference annotated with a red curly brace). There are no major local sources nearby. The higher terrain is impacted by more smoke from aloft, and the low level inversion keeps Neah Bay somewhat shielded.

Similarly, the Tacoma area ventilated out early this morning but the smoke clung on in the Puyallup valley (annotated with a black curly brace), located about 12 miles east.

Moral of the story: there can be legitimate differences for sharp spatial gradients.

Finally, this graphic from the National Weather Service in Spokane has a succinct message for all of eastern WA:

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