Contact: Barbara McGehan FOR IMMEDIATE RELEASE
(303) 497-6286 10/11/95
While ozone over the South Pole continues to decrease, the depletion is similar to last year, according to David Hofmann, acting director of the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo.
Hofmann believes that ozone depletion at the South Pole should level off over the next few years, and that the positive effects of the Montreal Protocol will cause a healing of the ozone layer, to begin early in the next century. The Montreal Protocol is a 1987 international agreement to reduce the global production of ozone-depleting substances.
On Oct. 5, balloon soundings indicated a total ozone value of 98 Dobson units (DU) in the column of air above the measuring site at the South Pole. Hofmann says this is only slightly less than the 102 DU recorded in October 1994 and somewhat more than the record low of 91 DU observed in October 1993.
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 deterioration occurs), the normal Dobson unit reading is about 275.
Although chlorine levels from manmade CFCs continue to increase in the Antarctic stratosphere, the increase is very slow and large changes in the magnitude of spring-time Antarctic ozone depletion are not expected. It is believed that the Montreal Protocol will result in a decrease in CFCs, and thus in stratospheric chlorine levels, but not until early in the next century.
In the past two years, Antarctic ozone has recovered from the effects of the Mt. Pinatubo volcanic eruption of 1991, particularly in the lower stratosphere (10-14 km, 6.2-8.7 miles), where most of the volcanic particles were located. Volcanic particles are believed to aid natural stratospheric cloud particles, which form in the cold, dark, Antarctic winter, in chemically preparing the Antarctic stratosphere for ozone depletion that follows when the sun comes up in spring. Absence of the volcanic particles reduces the chlorine conversion processes and reduces ozone depletion, according to Hofmann.
###Note to Editors: A TIROS satellite photo showing a false color representation of ozone amount over the Southern Hemisphere is available by calling NOAA Public Affairs: Barbara McGehan in Colorado at (303) 497-6286, or Jeanne Kouhestani in Washington, D.C., at (202) 482-6090.