Why is Utah's Air So Bad?

Air quality rarely reaches red, but this last week it was out of control

Utah. We claim to have “The Greatest Snow on Earth” but what about the worst air in the nation?

Currently three Utah cities are listed in the top five for worst air in the nation, according to AirNow.gov

We especially noticed this last week. After the snow cycle ended in the third week of January, the inversion began immediately to form. So what is causing it?

There is a relationship in the winter of deep snow cover, short days, how deep the inversion is and how bad the air quality becomes.

Check out this explanation from Good4Utah’s Chief Meteorologist Dan Pope.

Clear nights and deep snow cover, over all of Northern Utah, including the West Desert areas, allowed the already cold air to become even colder.

In the beginning of the high-pressure ridge, the inversion was deep. The top was between 7,000 and 7,500 feet. The visible and measurable pollution was being persistently released from the vehicles, industrial and other more natural sources. But, there was nearly 3,000 feet of volume above the ground for this pollution to expand into.

Light winds that go up-mountain during the daytime and down-mountain in the nighttime tend to converge pollutants in the morning and early afternoon in the middle of the valleys. You hardly would recognize this, and with light winds above the valley during the high pressure ridge (30,000 feet up), only a slow build-up pollution was noted.

Let me refer mostly to the PM 2.5 pollution from now on.

These very small particulates that are tiny enough when you breathe them in--that they can easily get caught in your lungs. They are also small enough to be pushed from your lungs into your bloodstream. They are dangerous for anyone to breath. Period.

By the middle of the last week of January, high pressure above the Great Basin was pushing down on the valley inversions, and the depth of the inversion shrunk to near 5,500 feet.

The volume that the PM 2.5’s were accumulating into went from close to 3,000 feet to between 700 and 1,000 feet. We lost 2/3rds of the of that volume, so everything that was up there 3,000 feet above us was pushed into less than 1,000 feet of volume. 

All of the sudden, air quality crashed from green or yellow to orange and red in a very short period of time. In fact, by January 30th through February 2nd, red air quality was rampant. 

On February 1st and 2nd, the large scale wind pattern, coupled with a weak storm that brought snow and rain showers to the Wasatch Front started blowing winds out of the south. BYU Provo reached 50 degrees on February 1st. Southerly winds pushed the red air quality out of Utah County and the west side of the Salt Lake Valley.

The same happened on February 2nd. However, even though the inversion was shallow, the pollution that was in Utah and western Salt Lake Counties moved north, rolling on top of the PM 2.5’s already collecting in Box Elder and Cache Counties. The deep, record breaking snow cover in these areas was keeping temperatures cold; and now we were adding pollution being siphoned northward from Utah, Salt Lake and Davis Counties into Weber and especially Box Elder and Cache Counties.

On February 2nd, Utah and Davis Counties broke into green air quality, while Salt Lake County remained Orange (likely due to the greater population and number of vehicles and industry in the area). Box Elder and Cache Counties crossed the red threshold and stayed there, longer than Utah and Salt Lake Counties did in the beginning.

What causes the inversion to clear up?

A weak storm will stir up the inversion this weekend, but it won’t have the energy necessary to clear the stubborn inversion in Cache Valley and possibly to some degree for Box Elder County. It takes a very strong wind or very cold air above the valley to “turn over” an inversion. The storm coming in Monday and Tuesday has both of those ingredients. The air will be cold enough that air will rise from the valleys to well over 25,000 feet. If Cache Valley doesn’t clear out completely on Saturday, it will on Monday and Tuesday. And for the rest of the Wasatch Front, things are already looking much better.

To check the latest air quality conditions click here.


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