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Tom Smart, Deseret Morning News
Smog shrouds the Wasatch Mountains Monday as horses work out at the Francisco Zamora Equestrian Center in West Jordan. People may want to limit outside activity.

The Oquirrh Mountains disappeared and the eastern foothills were vanishing. That was the illusion Monday afternoon, looking west and east from downtown Salt Lake City.

The reason: a pall of air pollution.

Bottled up by a temperature inversion, the gunk grew so dense that the Utah Division of Air Quality imposed the season's first "red" no-burn restrictions Monday afternoon for Salt Lake and Davis counties. This category, reserved for the least healthy air, outlaws use of wood-burning stoves and fireplaces.

It is to remain in effect today at least until the mid- to late afternoon when a weather system is expected to blow out the pollution.

The division designated a "yellow" condition, meaning the air isn't quite as bad and that residents should voluntarily refrain from burning wood, for Utah and Weber counties. The Bear River Health Department said Cache County is in a "yellow" condition.

In all of these except Weber County, health advisories are in place.

Northern Utah is suffering through its longest stretch of bad air this year. "We did have a spell on Thanksgiving" in which a yellow alert was issued, said Robert Dalley, manager of the Air Monitoring Section, Utah Division of Air Quality. But, he added, "it only lasted a couple of days."

And it never reached the red level declared on Monday.

The inversion set up about a week ago, Dalley said. The atmosphere accumulated so much particulate pollution that the yellow wood-burning advisory was issued Friday. Health advisories were issued Saturday.

Hope is on the horizon. Mike Seaman, meteorologist with the National Weather Service, said a front this afternoon, assuming the wind is strong enough, should disperse the pollution.

The green-yellow-red pollu- tion levels are geared toward reducing exposure to harmful particulate emissions. Green conditions are declared when the air is clear and there are no restrictions on wood burning. Yellow means people should voluntarily refrain from using wood- or coal-burning stoves or fireplaces. Red means the air is so bad that such use is forbidden until conditions improve.

"You are asked to drive as little as possible during red and yellow days because cars contribute significantly to the area's air pollution," a press release from the division says.

Industry also is expected to do its part by reducing emissions, if possible.

In Salt Lake, Davis, Utah and Cache counties, people with sensitivities to air pollution should avoid prolonged or heavy exertion outdoors. These include anyone with respiratory or heart disease, plus the elderly and children.

Twice a day, morning and afternoon, conditions are updated on the state's Air Pollution Hotline. The division offers these numbers for residents to get more information: Salt Lake and Davis counties, 975-4009; Utah and Weber counties, 800-228-5434; Cache County, 435-792-6612.

E-mail: bau@desnews.com