David E. Steitz
Headquarters, Washington, DC                       Oct. 6, 1999
(Phone:  202/358-1730)

Cynthia O'Carroll
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/614-5563)

RELEASE:  99-116

ANNUAL DEPLETION OF ANTARCTIC OZONE RESULTS ARE IN:
'OZONE HOLE' SMALLER THAN LAST YEAR

     A NASA satellite has shown that the area of ozone depletion 
over the Antarctic -- the well-known ozone "hole" -- is a bit less 
in 1999 than it was last year.

     "This Antarctic year's ozone depletion area, or ozone 'hole,' 
is very large, but slightly smaller than that of 1998," said Dr. 
Richard McPeters, principal investigator for the instrument that 
made the measurements.

     This year's study found that an ozone "low" had formed 
between New Zealand and Antarctica on Sept. 17.  This sort of 
ozone low, commonly referred to as a "mini-hole," is a result of 
the redistribution of ozone by a large weather system.  The "mini-
hole" moved eastward along the rim of the Antarctic "ozone hole" 
for a number of days after Sept. 17.

     Preliminary data from the satellite show that this year's 
Antarctic ozone depletion covered 9.8 million square miles on 
Sept. 15.  The record area of Antarctic ozone depletion of 10.5 
million square miles was set on Sept. 19, 1998.  

     The ozone levels are expected to decrease over the next two 
weeks.  The lowest amount of total-column ozone recorded to date 
this year was 92 Dobson Units on Oct. 1.  In contrast, ozone 
levels of 90 Dobson Units were observed at one point last year.  
Dobson units measure how thick the ozone layer would be if all the 
overhead ozone molecules in a column of atmosphere could be 
brought down to the Earth's surface.

     Globally, the ozone layer averages approximately 300 Dobson 
Units, which would correspond to a layer about 1/8th of an inch (3 
millimeters) thick at the Earth's surface, about the thickness of 
two stacked pennies.  In contrast, during the annual Antarctic 
ozone "hole," the amount of ozone in the ozone "hole" is about 100 
Dobson Units, about 1/25th of an inch, or approximately the 
thickness of a single dime.

     The slightly decreased size of the ozone "hole" from last 
year is not an indication of the recovery of Antarctic ozone 
levels.  The current year-to-year variations of size and depth of 
the ozone "hole" depend primarily on the variations in 
meteorological conditions.

     The Antarctic ozone losses are caused by chlorine and bromine 
compounds released by chlorofluorocarbons (CFCs) and halons.  Due 
to international treaties regulating the production of these 
gases, the amount of chlorine in the stratosphere is close to 
maximum value and, in some regions, is beginning to decline.  In 
the next century, chlorine-induced ozone losses will be reduced as 
chlorine amounts throughout the stratosphere decline, and ozone 
levels will begin to recover.  The actual rate of recovery will 
likely be affected by the increasing abundance of greenhouse gases 
in the atmosphere.  Detecting the recovery of the ozone hole will 
require a number of years of measurements.

     Ozone molecules, made up of three atoms of oxygen, comprise a 
thin layer of the atmosphere that absorbs harmful ultraviolet 
radiation from the Sun.  Most atmospheric ozone is found between 6 
and 18 miles above the Earth's surface.

     Ozone shields life on Earth from the harmful effects of the 
Sun's ultraviolet radiation.  Scientists and others have a keen 
interest in ozone depletion. Increased amounts of ultraviolet 
radiation that reach the Earth's surface due to ozone loss might 
increase the incidence of skin cancer and cataracts in humans, 
depress the human immune system, harm some crops and interfere 
with marine life.  

     These measurements were obtained between mid-August and early 
October using the Total Ozone Mapping Spectrometer (TOMS) 
instrument aboard NASA's Earth Probe (TOMS-EP) satellite. NASA 
instruments have been measuring Antarctic ozone levels since the 
early 1970s.  Since the discovery of the ozone "hole" in 1985, 
TOMS has been a key instrument for monitoring ozone levels over 
the Earth.

     TOMS ozone data and pictures are available on the Internet:  

      http://toms.gsfc.nasa.gov or http://www.gsfc.nasa.gov/

     TOMS-EP and other ozone-measurement programs are important 
parts of a global environmental effort of NASA's Earth Science 
enterprise, a long-term research program designed to study Earth's 
land, oceans, atmosphere, ice and life as a total integrated 
system. 
                             -end-

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