SALT LAKE CITY The air pollution that smothered mountain valleys in northern Utah for more than a week made a dramatic improvement Sunday.
Regulators say the pollution could build up again later this week, however, and they kept a ban on wood burning in place.
The relief came courtesy of a winter storm moving across Utah. Winds ahead of the storm finally loosened an icy fog that was trapping tailpipe and other emissions in mountain valleys.
Doctors declared a health emergency, but Gov. Gary Herbert refused to follow suit with a decree of his own. The doctors called for lower highway speed limits, curbs on industrial activity and free mass transit.
Soot along the greater Salt Lake region topped out at up to 130 micrograms per cubic meter last week. That was more than three times the clean-air limit set by the U.S. Environmental Protection Agency. But on Sunday, the count of extremely fine particulates was down to 10 micrograms per cubic meter in Salt Lake and Davis counties.
Still, the Utah Division of Air Quality issued a mandatory no-burn day Sunday for Box Elder, Cache, Davis, Salt Lake, Tooele and Utah and Weber counties.
Regulators asked industries to minimize air pollution emissions and urged people to limit discretionary driving.