Aug. 1, 1996
									            Contents embargoed
									            until 12:00 Noon
Doug Isbell
NASA Headquarters
Washington, D.C.  20546
(phone:  202/358-1753)

Allen Kenitzer
Goddard Space Flight Center
Greenbelt, Md.  20771
(phone:  301/286-8955)



RELEASE: 96-047


SURFACE ULTRAVIOLET RADIATION LEVELS HAVE INCREASED FROM 1979 
TO 1992

	Solar ultraviolet radiation reaching the Earth’s surface has increased over large 
regions of the planet during the past 15 years, as the amount of total ozone in the 
atmosphere has decreased, according to a scientific paper published in the Aug. 1 
issue of Geophysical Research Letters.

	Scientists and others have a keen interest in ozone depletion, given that the 
increased amounts of ultraviolet radiation that reach the Earth’s surface because of 
ozone loss, have the potential to increase the incidence of skin cancer and cataracts 
in humans, harm some crops, and interfere with marine life.

	Ozone, a molecule made up of three atoms of oxygen, is found in the 
atmosphere between the ground and about 37 miles (60 kilometers) in altitude.  
Ozone absorbs ultraviolet radiation from the Sun and shields life on Earth from its 
harmful effects.  


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	Because the risks of further increases in ultraviolet radiation are serious, 
scientists around the world are working to improve our current understanding of how 
much of the ozone-related change in the atmosphere is caused by humans and how 
much is attributable to natural processes, such as shifts in atmospheric dynamics, 
variable volcanic activity or long-term cyclical changes in solar radiation.

	This finding, which is derived from extensive analysis of data from the Total 
Ozone Mapping Spectrometer (TOMS) aboard NASA’s Nimbus-7 satellite, is based on 
the known relationship between atmospheric ozone depletion and the resulting 
decrease in protection from ultraviolet radiation (UV-B, 290 nm to 320 nm).  The 
accuracy of the TOMS-derived surface UV-B values has been validated by comparison 
with several ground-based spectrometers in Canada, New Zealand, and South 
America.

	“The increases are largest in the middle and high latitudes, where most people 
live, and where the majority of the world’s agricultural activity occurs,” said Dr. Jay 
R. Herman, an atmospheric scientist at NASA’s Goddard Space Flight Center, 
Greenbelt, MD, and the lead author of the paper, “UV-B increases (1979-1992) from 
decreases in total ozone.” 

	In the paper, Herman finds that annual average UV-B exposure has increased 
by 6.8 percent per decade at 55 degrees north latitude, where major populations in 
countries such as England, Germany, Russia and Scandinavia reside.  At 55 degrees 
south latitude, which includes the southern portions of Argentina and Chile, the 
increase has been 9.9 percent per decade.  In North America the changes are smaller 
since most of the population lives below 55 degrees.  The UV-B changes for regions 
near the Canadian border show about a 4% increase per decade.

	“This confirmation that we can use a space-based sensor like TOMS to 
measure long-term global surface ultraviolet radiation levels represents a very 
powerful new tool for Earth Scientists and others to use both now and in the future,” 
said Dr. Robert Harriss, Director of the Science Division, of NASA’s Office of Mission 
to Planet Earth, Washington, D.C.

	Studies have shown that ozone depletion is caused by complex, coupled 
chemical reactions.  Emissions of human-manufactured chlorofluorocarbons(CFCs), 
which break down into ozone-depleting forms of chlorine, have led to reduced 
atmospheric ozone.  If unchecked, the continued build-up of CFC’s, historically used 
in refrigeration, electronics, and insulating materials, could lead to additional ozone 
loss worldwide.  However, international agreements signed in recent years have led to 
sharply reduced usage of CFC’s, which should lead to the slow recovery of the ozone 
layer.  Already there are initial indications that the reduced CFC usage is effective in 
slowing the buildup of tropospheric chlorine.



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	During its lifetime on the Nimbus-7 satellite, the TOMS helped make “ozone” a 
household word through its false-color images of the Antarctic “ozone hole,” which 
forms from September through November each year.  The NASA-developed 
instrument, which measures ozone indirectly by monitoring ultraviolet light scattered 
by the atmosphere, produces daily maps of the global distribution of ozone in Earth’s 
atmosphere and of the surface UV.

	Another Total Ozone Mapping Spectrometer was launched on July 2, 1996, 
aboard a dedicated NASA Earth Probe satellite called TOMS-EP.  To ensure that such 
ozone data will be available throughout the next decade, NASA plans to continue the 
TOMS program using both U.S. and international spacecraft.  Japan's Advanced 
Earth Observing Satellite (ADEOS) will carry a TOMS into orbit during its scheduled 
launch on Aug. 16, and a fifth TOMS Instrument is being prepared for flight in 2000 
using a Russian spacecraft.

	TOMS is part of NASA’s strategic enterprise called Mission to Planet Earth 
(MTPE), a long-term, coordinated research effort to study the Earth as a global 
system.  The TOMS instruments are managed by the Goddard Space Flight Center for 
NASA’s Office of Mission to Planet Earth, Washington, DC.

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