The recipe is really simple.

Just add a high-pressure system with seasonally hot temperatures, emissions from several hundred thousand cars, a lack of upper-atmospheric winds and, voila, the 15th health advisory in Utah in 1998.This is also the 13th voluntary no-drive day this summer. At an air monitoring station in Salt Lake City, ozone levels were measured at 0.098 parts per million, said Bob Dalley, manager of the state air monitoring section. In July 1997, the U.S. Environmental Protection Agency issued tougher new ozone standards, which consider a reading of 0.085 ppm as unhealthful.

The call for commuters in Salt Lake and Davis counties to find alternative forms of transportation - car pooling, public transit or telecommuting - was issued Wednesday by the Utah Department of Environmental Quality.

Unhealthful levels of ozone are caused by a combination of sunlight, emissions from autos and industry, and high temperatures.

With temperatures expected to push the century mark Thursday and Friday, the DEQ is warning the elderly, young children and people with existing heart or respiratory ailments to keep their activities to a minimum. Officials say reducing physical exertion and outdoor activity during the midmorning and afternoon hours is especially important.

David Hogan, a forecaster for the National Weather Service, said that relief is in sight over the next few days.

"The problem we've seen in the last couple of days is the high pressure air is compacting all of the pollutants from cars. That makes it tough to mix the junk out of the atmosphere," Hogan said.

The forecast calls for high winds to move in Friday and isolated showers over the mountains on Saturday, Hogan said.

Dalley said the voluntary no-drive days have not worked out exactly the way he would like.

"We haven't seen a landslide response from the public," he said. "If people were only to double up when they drive to work, we could cut the air emissions in half."

The DEQ has a hotline that gives the pollution and ozone forecast for each day. The information is updated daily and gives instructions ranging from the best time to fuel your car to when air quality is best for exercise. In Salt Lake County, call 533-7239.