Tuesday, September 5, 2017

A Smoky Day Ahead

Over the past few days Utah has fortuitously been located just to the south of some thick, smoky air, but that changed overnight as the winds shifted.  The Wasatch Mountains this morning look more like the Great Smokies.

That photo was taken about 7 am.  As things stand now (8:20 AM) I can barely see the base of the Oquirrh Mountains from my office at the University of Utah.

It's a bit too early to get a good look at the smoke in visible satellite imagery, but we can see it very clearly in ceilometer observations.  A ceilometer is an instrument that sends out a laser pulse and measures the amount and delay of the signal returned to ascertain cloud base height.  Smoke and other particles in the atmosphere, known as aerosols, also scatter some energy back, which is known as backscatter.

The plot below shows a profile of backscatter recorded from a ceilometer at the University of Utah Mountain Meteorology laboratory at Red Butte Canyon.  Time increases to the right and is in MDT.  Note the arrival of dense smoke denoted by the change in color from green to yellow at around 3 AM MDT.  You can also see that the smoke moved over this site first aloft and then near the surface.

Source: MesoWest
Today we will have an air quality double whammy of elevated PM2.5 and ozone.  PM2.5 at the Mountain Meteorology Lab has been running near or above 25 ug/m3 since about 4 MDT (consistent with the plot above).

Source: MesoWest
That rates as "moderate".  Keep in mind, however, that ozone levels the past few afternoons have been at or above the unhealthy threshold (red shading below).
Source: Utah Division of Air Quailty
I'm not sure where we'll end up today.  Sometimes the chemicals accompanying smoke enable a boost in daytime ozone production.   Keep an eye on things if you have concerns.  I'm planning on taking a day off from exercising.


  1. Has there been any attempt to create an integrated AQI that incorporates both the PM2.5 and Ozone values? I believe that the AQI policy is to use the readings from the worst pollutant. Seems nonsensical on days where both are contributing exposure risk.

    1. I don't know. Perhaps someone in the know can comment.