Tuesday, January 6, 2015

Dirty Air Remains

Although there was a beautiful sunrise this morning, looking down into the valley from the upper Avenues reveals that a thin lens of polluted air remains.

Yup, this is a great case of the partial mix out.  The winds pick up and it cools off just enough to mix things out at the benches and to improve the air quality somewhat, but not enough to get us to pristine air.

As things stand this morning, there's still a fairly strong inversion at low levels over the valley where temperatures increase from 1.2ºC at the surface to 8ºC at 850 mb (about 5300 feet).  The pollution is confined primarily to the lower portion of this inversion layer along the valley floor.

Source: SPC

The Trax-mounted PM2.5 sampler this morning has been moving along the green line from the airport to West Valley City.  Concentrations are solidly in the moderate air quality category.

PM2.5 concentrations during the hour ending at 8:05 AM MST.  Source: http://meso1.chpc.utah.edu/mesotrax/cgi-bin/mesotrax_map.cgi
The University of Utah campus is sitting right at the top of the pollution layer and this has resulted in some very interesting readings at our mountain meteorology lab near the mouth of Red Butte Canyon.  In the plot below, I've highlighted in red periods when the wind is NOT consistently from the east.  You will notice that these tend to be characterized by somewhat higher PM2.5 values (bottom graph) and polluted air.  When the wind becomes steady and out of the east, which means it is originating from Red Butte Canyon and the surrounding foothills, PM2.5 values drop pretty much to zero.  Note how the PM2.5 values rise when the easterlies slacken.  There is a very nice example of this just after 4 am when the easterlies weaken, the flow shifts to west and PM levels spike to 12 ug/m3.

Kudos to everyone at the U who has contributed to collecting all this great PM2.5 data.  It's very illuminating!

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