Inversions and pollution: what’s the difference?

Dec 4, 2023, 12:11 PM | Updated: 1:37 pm

air quality...

FILE -- With the Wasatch Mountains to the left, a layer of haze and smog covers the Salt Lake Valley on Wednesday, Dec. 13, 2017. (Stuart Johnson/Deseret News)

(Stuart Johnson/Deseret News)

SALT LAKE CITY — According to the Utah Department of Air Quality, the average Utah winter brings about five to six multi-day inversions. 

Similar to pollution, inversions can lead to unhealthy air quality. Chronic exposure can lead to diseases such as stroke, ischaemic heart disease, and lung cancer, according to the World Health Organization

Air pollution is defined by the World Health Organization as contamination of the air by “any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.” 

Inversions and pollution

An inversion, on the other hand, is a phenomenon that can trap pollution close to the valley floor. The Utah Division of Air Quality said that “surface temperature inversions play a major role in air quality, especially during the winter.”

KSL Meteorologist Matt Johnson said that “inversions have existed since the beginning of time.” He added that “inversion[s] trap pollution. Pollution does not cause inversion.” 

According to the DEQ, warmer air normally sits closer to the ground. But when an inversion happens colder air gets trapped closer to the ground. 

When that happens, pollutants are also trapped closer to the valley floor. Pollutants can be vehicle or factory emissions, or other compounds such as sulfur dioxide and lead, according to the DEQ

They cause that thick fog that appears to erase the mountains. 

The science behind reversed air temperatures

According to the DEQ, air temperatures get reversed for a few different reasons. First, longer winter nights allow the ground more time to cool. The longer cooling period results in a lower surface temperature. The lower position of the sun also impacts the cool temperatures. 

Second, calm winter winds reduce the mixing of cold and warm air. When cold and warm air aren’t mixed, pollutants aren’t dispersed

The DEQ said that it is common for Utah to see inversions following snowstorms. Additionally, mountains can make inversions stronger. The Wasatch and Oquirrh mountains, as well as Traverse Mountain, all form a basin that traps cold air. According to the DEQ, the basin formed by the mountains shields it from wind that might otherwise clear inversions out of the Salt Lake Valley. 


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Inversions and pollution: what’s the difference?