Worst Air Quality in the Nation: Blame the Inversion

We can be proud (I guess) that the Northwest has some of the worst air quality in the nation--or so says the U.S. government's AirNow website:

And, in fact, Puget Sound Clean Air Agency has burn bans on right now in Snohomish and Pierce counties.

The region, strangely enough, is the push of warm air aloft.  The warming has been profound aloft during the past 48h, with the air warming 15-25F in layer starting a few thousand feet above the surface.   At Paradise on Mt. Rainier (5500ft) it has become nearly spring-like, with temps reaching near 50F.

With warming aloft, with cooler air stubbornly holding in at the surface, we have seen the development of a strong inversion (temp increasing with height).  To illustrate, here is the lower atmosphere temperature soundings on Monday morning from 1 AM to 8 AM.  Temperature increased 8C (14.5F)  in 500 meters (roughly 1600 ft) during that time period.

Inversions are very stable layers and tend to trap pollution near the surface.  Here are the particulate observations (PM2.5) for the last week for Seattle Duwamish, Tacoma, Lake Forest Park in N. Seattle, and Marysville in Snohomish County.  The trend is clearly upwards.

You notice that there is a big daily variation in air quality.  Better during the day and gets bad rapidly in the evening--worse around midnight.

A few things contribute to this diurnal (daily) variation.   First, folks come home around dinner time and crank up the heat...which pushes combustion products into the air.  Then around midnight the heat is turned off and air quality improves.  You will see a smaller secondary peak around 6 AM when the heat comes back on for some.   Another issue is meteorology.  Sun during the day warms the earth and causes some mixing in the vertical (like in your cereal pot).  This improves air quality.  At night, with nocturnal surface cooling, the inversion strengthens and air quality degrades.

We will have to deal with degraded air quality for a few days...later this week, the storms, rain, and wind return.