Contact: Barbara McGehan FOR IMMEDIATE RELEASE
Dave Hofmann 10/14/97A complete loss of ozone between the altitudes of 14 and 20.5 km (9-13 miles) was observed recently by National Oceanic and Atmospheric Administration scientists at the South Pole. This is the broadest region and highest altitude in which complete ozone destruction has been observed during the Antarctic springtime ozone hole period to date.
According to David Hofmann, director of NOAA's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo., this extension in altitude of total depletion is probably due to continued increases of stratospheric chlorine from human-induced CFCs (chlorofluorocarbons).
While chlorine-containing gases have begun to decline in the lower atmosphere due to restrictions placed on them by the Montreal Protocol and its subsequent amendments, it will take some time for chlorine to disappear from the stratosphere. (The Montreal Protocol is an international agreement to limit ozone-damaging compounds that was originally signed by the United States and 22 other nations in1987, and subsequently revised and amended.) However, the expectation is that chlorine levels in the upper atmosphere will peak near the turn of the century, resulting in the slow recovery of the ozone layer, Hofmann said.
Balloon soundings at the South Pole indicate that total column ozone reached a minimum of 112 Dobson units on Oct. 8. This is similar to what springtime minimum readings have been in the past few years, indicating that large changes in the magnitude of springtime Antarctic ozone depletion are not occurring. Dobson units are a measure of the thickness of the ozone layer, which has the ability to absorb ultraviolet light. Prior to the springtime period in Antarctica, when ozone depletion occurs, the normal Dobson unit reading is about 275-300.
Observations from instruments aboard a NOAA satellite indicate that the size of the Antarctic ozone "hole" approached 22 million square kilometers in early October. This is comparable to the recent size as observed by the NOAA-9 instrument in 1995 and 1996 at the same time of the season.
Note to Editors: Balloonborne ozone profiles at the South
Pole from the Climate Monitoring and Diagnostics Laboratory are available
at:
http://www.cmdl.noaa.gov/ozsondes/spo/ozppp.html