Generally, air quality is very good over western Washington due to the long over-water trajectory of air reaching our shores, but today there is a modest degradation (yellow colors) over some of the most populated areas (see graphic). Why? Lots of folks like to rev up their fireplace or wood stove for the holiday, and with cold air at low levels and high pressure aloft, a layer of stable air is found aloft.
This stable air is indicated by a layer from roughly 50-m to 300 m aloft over Seattle where temperatures stay the same or warming a bit with height (inversion).
As noted above, our air quality is relatively good because winds in the midlatitudes are from the west and thus our air comes over the vast Pacific Ocean--although a small amount of Asian air pollution does get across. To illustrate our source of air today, below are
backwards air trajectories (paths of air in space) for air parcels ending near the surface, 500 m aloft, and 1500 m aloft from the wonderful NOAA Hysplit system. At all levels, our air came from the north Pacific, with the air parcels rising from near the surface to around 7000 ft before descending again over us.
A summary of air quality in Seattle for the past year is summarized below (green is good air quality as shown in the legend above). Mostly green (good quality) with a sprinkle of yellow (moderate) days like today.
The same plot for Los Angeles show many more moderate days and occasional poor air quality periods (dark orange). Beijing would be orange or red nearly all the time.
I have a visitor from Beijing and she is impressed with the wonderful quality of our air. Something to be thankful of. U.S. air quality improved substantially starting in the mid-70s due to a bipartisan national program to clean-up our air (e.g., U.S. Clean Air Act, EPA, etc.). If only we could be wise enough to foster a bipartisan effort to deal with increasing levels of greenhouse gases.
from Cliff Mass Weather Blog http://ift.tt/2iuLZIe
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