Thursday, December 26, 2013

Pollution Doesn't Take a Holiday

A truly spectacular airmass pushed into the Salt Lake Valley and gave us a remarkably clear Christmas Eve.  As the sun was setting and Santa approached, one could breath easy for their long winter's nap. 
4:30 PM MST Christmas Eve, 2013
However, it didn't take long for a veil of smog to begin to develop.  On Christmas, air quality was still good, but one could begin to see the effects of all the yule log burning on the visibility over the valley (I'm not sure if wood pollution is the problem, but "yule log burning" seemed to fit well there).  Note in particular the smoggy tint in the right-hand side of the image below.  
4:30 PM MST Christmas
The view from the Avenues Foothills also showed a veil of Christmas smog hanging over the valley on an otherwise unbelievably spectacular day.
A thin veil of Christmas smog over the Salt Lake Valley
The latest observations from the Division of Air Quality shows that the hourly PM2.5 concentrations peaked last night at 33.5 ug/m3 and the 24-h average PM2.5 now sits at about 15 ug/m3.  Although these are only in the moderate air quality category, this case provides an example of just how fast we see our air quality deteriorate after the valley has been flushed out and the inversion builds in.  From good to moderate air quality in 24 hours.  Pollution doesn't take a holiday. 
Source: Utah Division of Air Quality
There is, however, a small Christmas gift on the way.  The inversion will strengthen today and probably reach peak intensity tomorrow.  On Friday night through Saturday morning, the models are calling the ridge to shift just far enough upstream to let a weak front push through Utah.    

Hopefully this will give us at least a partial mix out, if not better.  


  1. There is often high ozone values above snow in regions with in Utah.
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  2. Love your blog. Thanks for all the information.
    I have a very practical question about air quality during an inversion. We're in Centerville, about 4300 ft. elevation. I need to exercise (I'm old) and I don't need lungs full of gunk so I'm looking for ways to get to clean air, daily. If I drive up to the Bountiful Temple to get above the smog layer, but I'm not quite above it, is the air in the smog layer less smoggy the higher I get, or actually more smoggy. In other words is there a level where the smog stops and clean air begins, or does it just gradually improve the higher you get. Sometimes I've wondered if maybe the smog actually thickens up at higher elevations (elevations lower than the warm layer). Am I clear? I want to be clear. I want to breathe clear!!

    1. I hesitate to generalize because every inversion is different, but there is evidence that at least in some inversions the PM2.5 concentrations do decrease from valley to bench levels (e.g., That being said, this is no guarantee that the air on the bench in any given event is "healthier" and there may be some inversion events where bench-level air quality is as bad as it is on the valley floor.

      A basic problem with air quality monitoring in the valley is that we have real-time data from only one site and clearly there is a lot of spatial variability. Given the seriousness of the problem we have, we should at least have real-time sites on the benches and probably multiple locations on the valley floor so that citizens can make informed decisions of the type you describe.

      As I write this, 24-hour PM2.5 levels at the real-time site in the Salt Lake Valley are now at 35.3 ug/m3 and the hourly values are at 61.5 ug/m3.

    2. Thanks for that, Jim. One thing for sure, we know how to pronounce ug/m ugh-um. Right?