PINEDALE - Ozone: It's good up high, but it's bad nearby.

The three-atomed gas known as ozone can be good or bad for people's health and for the environment, depending on its location in the atmosphere, scientists said during an ozone forum Tuesday night in Pinedale.

The Upper Green River Basin has registered at least slightly elevated levels of ozone in three out of the past four winters around Pinedale.

Federal regulations limit ozone air pollution to no more than 75 parts per billion during an eight-hour period. Ozone levels near the town of Boulder, in rural Sublette County, climbed to 122 parts per billion in February, a level higher than most urban areas.

The ozone spikes prompted Wyoming's Department of Environmental Quality to issue several ozone alerts this past winter that warned residents to limit strenuous or extended outdoor activities.

Fred Miller, a medical research professor at Duke University Medical School, said elevated ozone levels were thought to be strictly a summertime occurrence, usually in large metropolitan areas.

"With your situation and the levels I've seen … there is cause for concern, but not cause for panic," Miller said. "You can mitigate the risks of exposure."'

Within Earth's upper atmosphere, or stratosphere, the ozone layer extends upward from about six to 30 miles and protects life on Earth from the sun's harmful ultraviolet rays.

But at ground level within the troposphere, ozone is a potentially poisonous gas that can cause breathing problems in children, the elderly and in people with existing respiratory conditions.

Symptoms in adults who breathe in ozone include coughing, a sore or scratchy throat, fatigue, inability to take a deep breath and other symptoms similar to asthma.

Miller said the federal standard of 75 parts per billion is an extremely small amount and illustrates just how toxic ozone is.

"It does no good to wear a mask, because the particles can penetrate it … you'd have to use a full respirator to avoid" ozone exposure, which is unlikely, he said.

Exercise greatly increases the amount of ozone inhaled, he said.

"By exercising, you can take in 10 times the mass or more of ozone deep into the lungs," Miller said. "If an ozone episode occurs, you shouldn't really be outside exercising."

Miller said reducing certain "factors" during ozone episodes can reduce the potential dosage of ozone in humans.

He suggested staying indoors as much as possible, doing outdoor work or exercising in the morning because there are typically higher levels of ozone in the afternoon, and paying attention to possible symptoms of ozone. "Best of all, know your body," Miller advises.

Southwest Wyoming bureau reporter Jeff Gearino can be reached at 307-875-5359 or at gearino@tribcsp.com.