On Tuesday, the air quality in Salt Lake City was the worst in the United States, according to the National Weather Service.
And the filthy air is not likely to blow out until late next week, according to Monica Traphagan, a senior meteorologist at the National Weather Service’s Salt Lake City office.
According to Traphagan, the dense haze is caused when cold air is stuck in the valley, trapped between the Wasatch Range and the Oquirrh Mountains by a high-pressure system above.
As the air remains stagnant, she said, so does particulate matter from pollution creators — cars, oil refineries, factories and fireplaces.
Traphagan said the weather phenomenon — called an inversion — is common for the area, which over the years has had the worst air quality not just in the country, but in the world.
(Francisco Kjolseth | The Salt Lake Tribune) The rising sun begins to illuminate the Oquirrh Mountains as inversion conditions trap pollutants in the Salt Lake Valley on Monday, Jan. 12, 2026.
This inversion, however, might seem intense because Salt Lake City has not seen any major inversion events for several years, Traphagan added.
Already, the Utah Department of Environmental Quality has determined that the air in Salt Lake County is unhealthy for sensitive groups.
“Unfortunately, it’s likely to get worse,” Traphagan said. “Particularly, I think we’ll see in the next few days nighttime fog expanding.”
For the smog to end, Traphagan said Salt Lake City either needs strong winds or an influx of fresh cold air that can sink to the bottom of the valley and create air flow, flushing out the pollutants.
The next storm capable of cleaning the valley likely won’t hit until the end of next week, Traphagen said. A system on Thursday or Friday, however, might help to weaken the inversion at higher elevations.
In the meantime, Traphagan said there are several things people can do to protect themselves from the pollutants: