A Rare January Great Salt Lake Dust Event

The sun had not yet crested the Wasatch this morning when I awoke and when I looked out the window I saw this odd band of white extending at low levels through the western Salt Lake Valley.  

My first thought was what the hell is that.  It's too shallow to be a lake band and it doesn't look like fog.  I took a look at the weather observations and the relative humidity in that area was less than 60%.  What could it be. 

I then looked at PurpleAir thinking it might be dust, but even then the PM2.5 numbers didn't seem very impressive.  

I kept digging, soliciting the input of some meteorological friends.  Eventually, with some help of specialized observing sites, satellite imagery, and weather cams, it became clear that it was blowing dust originating from the exposed Great Salt Lake bed east of Antelope Island.  

A quick look at the evidence.  The most damning was a video of web cam images from the MesoWest web cam at Syracuse near the eastern end of the Antelope Island Causeway.  The view toward the southwest and Antelope Island clearly showed lofting dust in the northerly flow. 

Dust is sometimes hard to see in visible satellite imagery, but an increasing sun angle clearly showed dust pouring off the Farmington Bay area southward into the Salt Lake Valley with a well-defined plume over the central valley.  If you look carefully, you can see evidence of the plume over Utah Lake too.  

My colleagues in the Department of Atmospheric Sciences operate a study site on the Farmington Bay playa abut 7 km south of the causeway entrance.  It might be a bit upstream and east of the biggest dust emissions sources, but it has clearly shown some significant spikes in PM2.5 concentrations.  

I took a look at the PurpleAir data, however, and it didn't show much.  This was a bit of a headscratcher for me. The image below was grabbed at 12:06 PM and for the most part, it looks like good air quality. That was what I observed most of the morning.

However, the University of Utah and DAQ sensors told a different story.  The data below is from a bit before noon and those sensors showed areas with moderate air quality due to elevated PM2.5. At just before noon, the highest values were around 24 ug/m3 near and just north of Murray.  

I'm a fan of Purple Air, but there are sometimes absolute errors in their estimates and this seems to be such a case.  

Overall, this is a remarkable event.  I cannot recall such a strong, well defined, and long-lived dust emission event from the exposed lake bed of the Great Salt Lake in the month of January.  It took me a while after seeing the plume to convince myself it was happening, but it's hard to deny at this point.  It raises a lot of questions about dust emissions processes on the playa during winter.  I don't have a sufficient background in soil physics to speculate about what might be happening.