• Particulate pollution. Starting over the weekend, levels of PM-2.5 particulate pollution have been rising. "They're actually running the highest to the north, up in the Ogden area," he said.

Ogden has reached 36 micrograms of PM 2.5 pollution per cubic meter, while the health standard is 35. In Logan, the level was 29 and in Lindon, 30, he said. Salt Lake and Davis counties had a particulate reading of 27.6 as of 2 p.m. Monday. However, St. George recorded only 14 micrograms.

While ozone levels may decrease at night, Sprott said, particulates tend to stay high throughout the night.

Dr. Richard E. Kanner, a pulmonologist at University Hospital and a former chairman of the Utah Board of Air Quality, said the greatest concern "is primarily with people who have heart and lung disease." These people probably should minimize their activity so as not to inhale much of the pollution.

He had this advice for healthy people: "I'd play it safe and not go jogging in this mess."

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