Seattle's Worst 24h Air Quality on Record

Air quality in western Washington is very poor right now.

Incredibly, in central Puget Sound it is probably the worst in the nearly two-decade observing record of the Puget Sound Clean Air Agency for any time of the year.

I have been here a long time and I have never seen anything this bad.  The view from the Seattle SpaceNeedle Panocam is murky (see below)

And the view from my department is very limited...no mountains and can't even see across the Lake.

But now, let me really impress (or depress) you.  Below is a plot of 24-h average particulate concentration (PM2.5) in the atmosphere at the Puget Sound Clean Air Agency Duwamish site in Seattle.  The past 24-h was the worst on record for any time of the year.  Number two was the smoky period last summer.   

Historically, Seattle has its worst air in the winter from wood smoke and other combustion products, but today and last year were summer maxima from wildfires--very different animals.

The observing site in Tacoma also had its record in the past 24-h hours. 

So why did our near surface air quality get so bad so fast?  

Fires were burning for quite a few weeks in British Columbia, California and eastern Washington, but western Washington had clean air at low levels (off the Pacific) with smoke aloft.  But on Monday, surface high pressure started to build in north and east of us (see map), resulting in easterly and northeasterly flow over the Cascades that brought the smoke over and down the terrain into western WA--allowing smoke to get to the surface.

Surface map at 8 PM Monday

I ran some low-level air trajectories ending in Seattle at 11 PM Tuesday night (using the NOAA Hysplit system).  Air ending at 100 meters above the city came from smoky BC, while air at 1000 meters were from eastern WA--both sources of smoke. 

High pressure aloft amplified just offshore, resulting in strong downward motions in the lower atmosphere, which produced a subsidence inversion from the surface up to about 3000 ft.   The inversion (temperature increasing with height) was very obvious in the balloon soundings at Quillayute, on the WA coast, and from the Seattle profiler (see below).  Inversions act as atmospheric lids, preventing the smoke from mixing out during the day.

In short, we had the "perfect storm" for wildfire smoke around western Washington.  Lots of fires around us, a meteorological situation that pushed the smoke to low levels, and the development of an inversion that kept the smoke in place. 

As I write this (10 AM), the air quality  in Seattle is getting even worse (see plot)

Incredibly, historically bad air and unhealthy for all.  No running for me today.  Expect very slow improvement on Thursday.






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