When you think of smog, Los Angeles or Phoenix probably come to mind. But right now, the worst air in the country is actually hovering over Salt Lake City, and it could mean big changes for life there.

The Utah city known for its clear skies and white capped mountains is now choking on a heavy blanket of smog. The Environmental Protection Agency says this month Salt Lake City has the worst air quality in the country. Dr. Ellie Brownstein, of Utah Physicians for Healthy Environment, a civic organization, said, "If you can see it you probably don't want to breathe it. We've had a long string of this. It really doesn't give our lungs a chance to heal and do well."

The problem is caused by what's called a temperature inversion. When the valley surrounding Salt Lake City is colder than the sunny mountain areas above it. That warm air aloft acts like a lid, trapping the cold air and pollution over the city. Soot from car exhaust and industrial emissions creates the toxic smog.

The EPA cutoff for clean air is 35 micrograms of pollution per cubic meter. Salt Lake City hit 130 micrograms Wednesday last week.

More than 100 Utah doctors are calling on state leaders to declare a public health emergency. They want to lower highway speed limits to 55 and shut down incinerator-based businesses that cause industrial pollution.

Brownstein said, "If mass transit were free throughout the winter so people would be encouraged to use that we'd have less cars on the road, if we had a wood-burning ban in effect, that would be a huge amount less particulate matter that doesn't sit in the valley."

The Utah Governor's Office sent out a statement saying, "While the current air quality does not meet legal criteria to declare an official public health emergency, we should all be actively doing our part to minimize emissions."

For now, doctors are telling people not to exercise outdoors to avoid breathing the air.