Those prone to respiratory illness are cautioned to stay inside during the hottest part of the day, and commuters are asked to voluntarily choose mass-transit in an effort to decrease pollution.

The call to curtail the use of vehicles and other machines with internal combustion engines such as lawnmowers and generators is part of the Utah "Choose Clean Air" program, which runs each year from June 1 to Sept. 1.

The red-level designation applies to increased ozone levels that rise when pollutants react chemically in the presence of sunlight, according to the Utah Department of Health.

University of Utah professor and asthma doctor Wayne Samuelson said the increased ozone levels are a product of Utah's unique topography and the high temperatures.

Outdoor exercise should be done in the early mornings or the evenings when the temperatures decrease, he said.

"Really, the best thing that [people] can do is try to avoid the heat," said Samuelson.

The Utah Department of Health estimates that one in three Utahns experience some kind of respiratory problem during high pollution periods. Prolonged exposure to low levels of ozone has the potential to reduce lung function in a healthy adult by as much as 20 percent.

"Certainly, when the temperature is up as high as it's been, it is an added problem with lung irritation," Samuelson said.

July has historically been the worst month of the year for high ozone levels. A record 14 no-drive days were designated in 2003. There were 12 no-drive days in 2005.

Those wishing to volunteer to reduce pollutant emissions can:

* Carpool or use mass transit.

* Telecommute.

* Postpone errands that can wait, if it's a high pollution day.

* Drive your newest car.

* Avoid drive-through lanes.

* Use cruise control on the highway.

* Properly dispose of all hazardous household materials.

* Use water-based instead of oil-based paints.

* Keep all solvents and paints in airtight containers.

* Purchase Energy Star products or other energy-efficient appliances, home electronics, and lighting.

* Use a push mower.

For more tips, visit http://www.cleanair.utah.gov.

mwestley@sltrib.com