What is an inversion?
An inversion is a weather phenomenon that occurs typically during the winter months when the normal conditions of the atmosphere become inverted. Instead of having cool air above and warm air below, the air becomes inverted and a layer of cold air becomes trapped under a blanket of warm air. By having this 'blanket effect,' pollutants have no way of escaping and diffusing into the atmosphere. The cold air holds in pollutants and creates a harmful smog that can last for weeks at a time.
|
Why Utah?
Due to the geography of the Wasatch Front, the Salt Lake Valley is prone to inversions during the winter months. By having a "bowl shaped" valley, cold, dense air can be easily trapped under a sheet of warmer air and can cause an inversion to take place. When this happens, particles and pollutants become trapped and more concentrated. This leads to the build up of smog and creates poor air quality conditions across the valley.
In Utah, inversions are known to last for weeks at a time. The only way to disrupt an inversion is by a strong storm. |
Inversions can occur in places other than the Salt Lake Valley. Cities such as Los Angeles share the same geographic characteristics where the bowl shaped valley easily traps cold air, causing pollutants to become trapped and creating a thick layer of smog over the city.
In the photo to the right, there is a central valley that is surrounded by two mountain ranges. Cold air settles into the valley and creates a blanket over the valley. With the help of heavily populated areas with high levels of pollution (ie, Los Angeles), smog begins to build up and begins to settle into the valley. |
In Utah, it's not unlikely to see moderate to unhealthy air quality levels. Just this winter, Salt Lake County had 18 mandatory air action days (red air days) and 28 voluntary air action days (yellow air days) from December 2016 to February 2017 (Utah Department of Environmental Quality). This means that even people who do not have a preexisting condition, such as asthma, were asked to take caution and avoid going outdoors as much as possible.
|
To the left is a time-lapse map of the air quality of the Wasatch Front on January 31st, 2017. As you can see, air quality fluctuates throughout the day, but progressively becomes worse.
The yellow represents moderate conditions. The orange represents unhealthy air for sensitive groups. The red represents unhealthy air for all groups. |
|