Utah had the worst air quality in the US this morning

KAYSVILLE — Four Utah cities landed on the top 10 worst air quality list Thursday morning.

Kaysville, Utah, was the most polluted city in the U.S. at 5:34 a.m., according to IQAir. South Jordan, Saratoga Springs, and Midvale also landed on the list in the morning.

That ranking has since changed. At the time of publication, the top 10 most polluted cities were all in California.

The rankings will continue to change. Experts said it’s influenced by a number of factors.

What influences air quality?

Cold air doesn’t rise, it sinks.

So, when Utah experiences an inversion, cold air and pollutants are trapped in the valleys, according to weather experts.

Typically, if you’re at a lower elevation, you’re more likely to have polluted, stagnant air. It also depends on how close you are to pollution sources, like freeways and industrial sites, where emissions are higher.

Heather Holmes is an associate professor of chemical engineering at the University of Utah. She compared it to skiing down the fall line of a mountain.

“It’s like the path of least resistance,” Holmes said. “Cold air will just slide down the mountain slopes, and it will all end up at the lowest elevation. So it’s a mixture of where you’re located in terms of elevation … and then also your proximity to sources.”

She said that before sunset, when these Utah cities made it on the worst air quality list, the layer of air closest to Earth’s surface was at its lowest.

So the valley bowl we live in has a top on it, pushing down the air, giving it less room to mix.

It makes the pollutants more concentrated.

KSL meteorologist Devan Masciulli said wind plays a part too.

“It could’ve been a factor of Kaysville. It’s close to the highway and it could have been a factor of, hey, the wind just perfectly pushed a concentration right over to Kaysville at that time, and that increased their AQI to just a little bit higher than some of the other locations.”

Experts said don’t be surprised if other Utah cities make that top 10 list tomorrow or the next time we have an inversion.