Shuttle Mission to Check Ozone Levels

The countdown began Saturday for the launch of the shuttle Discovery on an atmospheric research mission that will include a check on ozone levels.

For the second year in a row, ozone levels this winter were 9% to 20% below normal over parts of the Northern Hemisphere, the World Meteorological Organization has reported. The eight-day mission set to begin Tuesday will help confirm if the ozone-depleting trend is continuing, said physicist Ernest Hilsenrath, an investigator of one of three ozone monitors aboard Discovery.

At ground level, ozone is a component of smog. But in the stratosphere, nine miles to 31 miles high, ozone is a safeguard against the sun’s burning ultraviolet rays.