Brian Dunbar
Headquarters, Washington, D.C.                   October 11, 1990
(Phone:  202/453-1547)

Dolores Beasley
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-2806)


RELEASE:  90-137

1990 ANTARCTIC OZONE HOLE EQUALS LOWEST PREVIOUS LEVELS


     Preliminary data indicate that depletion of stratospheric 
ozone over Antarctica is matching levels observed in 1987 and 
1989, the lowest ozone years recorded, NASA scientists said.

     Research by Dr. Arlin Krueger, Dr. Mark Schoeberl and Dr. 
Richard Stolarski of NASA's Goddard Space Flight Center, 
Greenbelt, Md., indicates the Antarctic "ozone hole" began 
developing in the last week of August when the normal, winter 
polar ozone levels started decreasing.  This was about one week 
earlier than the beginning of depletion in 1987 and 1989, though 
the timing of the start of the depletion has shown significant 
variability over the years.

     Ozone, a molecule made up of three atoms of oxygen, 
comprises a thin layer of the upper atmosphere that acts as a 
shield against harmful ultraviolet radiation from the Sun.  In 
the presence of sunlight, atoms of chlorine and other chemicals 
can strip an oxygen atom from an ozone molecule, leaving behind 
an oxygen molecule, which does not absorb the radiation.  Because 
of the catalytic nature of the reactions, each chlorine atom can 
destroy thousands of ozone molecules.

     The ozone hole is a large area of intense ozone depletion 
over the Antarctic continent that typically occurs between late 
August and early October.  The ozone hole has been monitored 
since 1979 using the Total Ozone Mapping Spectrometer (TOMS), an 
instrument on the Goddard-managed NIMBUS-7 spacecraft.

     Not only has the 1990 ozone hole matched the lowest levels 
previously observed, but ozone levels throughout the Southern 
Hemisphere has been as low as any previously recorded year.  
Scientists have observed previously that the ozone hole has 
followed a roughly biennial cycle, in which ozone depletion has 
been less severe in even-numbered years than in odd-numbered 
years.  The implications of such severe depletion in 1990 are 
uncertain, said Dr. Robert Watson, Chief of NASA's Upper 
Atmosphere Research/Tropospheric Chemistry Branch.  Year-to-year 
variability in ozone depletion appears to be related to the 
interplay of meteorological conditions and atmospheric chemistry, 
but the exact process is not definitively understood by 
scientists.

     NASA's programs for studying ozone depletion, managed by the 
Office of Space Science and Applications, will expand in 1991 
with the launch of another TOMS instrument aboard a Soviet Meteor 
Satellite and the deployment of the Upper Atmosphere Research 
Satellite by the Space Shuttle.  The just completed Space Shuttle 
mission, STS-41, carried the Shuttle Solar Backscatter 
Ultraviolet instrument (SSBUV), a device similar to TOMS that 
estimates ozone levels by measuring reflected ultraviolet 
light.  SSBUV collects data that are used to calibrate the TOMS 
instrument.