Local Pollution or Smoke?

Looking toward the central Wasatch Mountains from the Avenues Foothills 3:30 PM Friday 16 November 2018

A lot of people have asked me if the haze in the valley is smoke from the fires in California.  There is probably a small amount of smoke that is in our area, but for the most part, what you are seeing in the valley is pollution of our own doing.

The vast majority of the smoke from the California fires remains over the central Valley, Bay Area, and offshore Pacific ocean, although there is some that extends eastward across the Great Basin.  This is illustrated by the HRRR-SMOKE analysis below for near-surface smoke concentrations.  Note that the HRRR estimates near-surface smoke concentrations to be 4 ug/m3 or less over northern Utah.   

Source: ESRL

I'm not sure how much to trust that estimate, but let's go with it.  PM2.5 concentrations on the University of Utah campus today have been running around 14 to 20 ug/m3, much higher than the HRRR smoke estimates.  Note that over the past two days the values have fluctuated dramatically, dropping to as low as zero overnight and then rising during the day.  This reflects the development of a down-canyon flow in Red Butte Canyon (the observing site sits at the mouth of the canyon), which brings clean air from aloft (above the smog layer evident in the picture above) at night.  This is another reason why I'm skeptical about smoke being a strong contributor to our current pollution.  We simply don't have much evidence of high smoke concentrations aloft.

Source: MesoWest

Finally, November IS part of our wintertime smog season.  The sun angle right now is plenty low and comparable to that in late January.  Further, we do have a persistent cold pool in place over the Salt Lake Valley.  Yesterday afternoon, for example, a series of stable layers just above 5000 feet prevented pollution from the valley from mixing with the atmosphere aloft.  If there were snow on the ground, we'd have a whopper of an "inversion" event. 

Source: SPC

So, as I like to say, we have met the enemy and it is us.  The good news is that the weak cold front coming through late tomorrow should stir things up.  However, we go back to ridging early next week, so consider taking the bus or alternative modes of transportation if you can do it.