Thursday, January 2, 2014

Zombie Inversion

"The Fog" (1980)
I hope you enjoyed the comparatively clean air that we had this morning because air quality in the Salt Lake Valley has deteriorated markedly in the past two hours with smog filling the lower elevations of the valley.

Downtown from the Avenues Foothills @ 3:15 PM MST 2 January 2013
The decline is not only visually apparent, but also evident as a very dramatic and large increase in PM2.5 concentrations at the real-time sensor at Hawthorne Elementary School.

Source: Utah Division of Air Quality
The reason why the air pollution won't die appears to be fairly simple: The Great Salt Lake.  During the day, the lake is relatively cold and the air over the lake is relatively cold.  As a result, the inversion tends to be strongest and mixing tends to be weakest over the lake.  During the day, the airmass over the lake typically penetrates into the Salt Lake Valley, bringing along with it all that nastiness.  The leading edge of this airmass is called a lake-breeze front.  Today, the lake breeze front was accompanied by the huge spike in PM2.5 and, as shown below, a slight drop in temperature, shift in wind to WNW, and an increase in wind speed to about 5 miles per hour.  

Temperature, humidity, and wind traces at Hawthorne Elementary
This is one of the most dramatic lake-breeze fronts I've seen in terms of pollution and it is why we can now call this a Zombie Inversion, since it clearly does not want to die.

1 comment:

  1. This just makes the case for more sensor/data stations. I sit and watch the pollution roll in and out throughout the day, sloshing back and forth in the valley. I think with a decent network of sensors, we could not only understand the structure of pollution motion in the valley, but also watch advection and mixing in progress to identify specific sources.

    I'm still unsatisfied with my understanding of why the hourly data this morning looks like a sawtooth graph...