Air quality over the past three days has deteriorated as pollution has built up in the valleys and basins of northern Utah. Below are time series of PM2.5 (top) and wind direction, speed, and gust (bottom) from the University of Utah. PM2.5 concentrations at this site tend to fluctuate daily and are typically lower at night when there is easterly to northeasterly outflow from Red Butte Canyon and higher in the afternoon when there is westerly to southwesterly upslope flow from the Salt Lake City metropolitan area. You can see these swings very clearly below, with peaks in PM2.5 in the afternoon and valleys at night.
You can also see that the weak trough passage on Friday did provide some ventilation of the valley with PM2.5 concentrations on Saturday afternoon considerably lower than on Friday afternoon.
However, that was only a partial mix out and since then we have seen PM2.5 concentrations rise each day. Yesterday afternoon, we peaked at 63 ug/m3, well above the threshold for unhealthy for sensitive groups of 35.5 ug/m3.
While the area around the University of Utah sometimes gets a nighttime flushing out, that's not the case on the valley floor. Additionally, Friday's weak trough put less of a dent in the pollution at those lower elevations. Below are PM2.5 estimates from the PurpleAir site at the West Valley city Public Works. Except for some brief dips into moderate (yellow), PM2.5 has been consistently in or above unhealthy for sensitive groups.
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| Source: PurpleAir.com |
Finally, we can also look up Parley's Canyon. The observing sites at Mountain Dell have shown daily fluctuations. Clean air at night and in the morning, then a big increase in the afternoon as up-canyon flow transports the urban plume from the Salt Lake Valley. Yesterday in particular saw a huge spike to unhealthy levels. Best to skate ski in the morning.
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| Source: PurpleAir.com |
We're stuck with this through at least Thursday. A trough moving over the ridge Thursday night and Friday may stir things up a bit and possibly bring a little snow too. Let's hope it does as we need it.
Hi Jim. I have a question about air quality in the Salt Lake valley, and I haven't been able to find an answer to it that I have any confidence in.
ReplyDeleteWhile the current inversions are terrible, and I hope current effective solutions are implemented and future mitigations are successful, my question is about the history of air quality in the valley.
I have heard, and found some sketchy corraboration for the idea, that while awful, the current air quality problems in Salt Lake valley are much less awful than they were historically, say, early 20th century due to wood burning, or during the 70s and 80s due to dirty automobiles and industry.
Can you clarify this for me? Is it worse today, about the same, or better? Or is our history of tracking air quality too young to say for sure?
While anecdotal, this is a relevant read: https://www.deseret.com/2009/12/22/20360123/coal-fires-used-to-blacken-s-l-air
DeleteOne of my colleagues here used to have a graph showing the decline that you suspect. I haven't been able to find it quickly. He put it together several years ago. I may have posted it on the blog at one time or another. If you have the time, you could click on Air Quality in the subject cloud in the right hand nav bar and scroll through, or you could try a search. Whether or not that has continued is unclear.
ReplyDeleteMy hope is that electrification of the transportation system will help moving forward, but we will have to see.
The current situation would be worse, potentially much worse, with snow on the ground.
Jim