This photo of Paul Crutzen was taken in 1993
at a colloquium held at NCAR in honor of Paul's
lifetime achievements. The pioneering atmospheric chemist
was an NCAR scientist from 1974 to 1980 and has been
a frequent visitor since. (Photo by Carlye Calvin.)
11 October 1995
Twenty years of study on the ozone layer have resulted in the first Nobel Prize ever awarded to atmospheric chemists. Receiving the 1995 Nobel Prize in Chemistry are Paul Crutzen (Max Planck Institute for Chemistry, Mainz, Germany), Mario Molina (Massachusetts Institute of Technology), and F. Sherwood Rowland (University of California, Irvine).
All three scientists are regular visitors to the Atmospheric Chemistry Division (ACD) of the National Center for Atmospheric Research (NCAR), which is operated in Boulder, Colorado, by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation. The three honorees have collaborated with NCAR scientists for years. Crutzen was director of ACD from 1977 to 1980, and he and Molina serve on ACD's advisory panel.
In announcing the award on 11 October, the Royal Swedish Academy of Sciences noted that "by explaining the chemical mechanisms that affect the thickness of the ozone layer, the three researchers have contributed to our salvation from a global environmental problem that could have catastrophic consequences."
Although the layer of ozone in the earth's stratosphere--the region 12 to 20 kilometers high (8 to 12 miles)--is relatively thin, it is crucial to life on earth because it absorbs the majority of the sun's ultraviolet radiation before it reaches the earth. Ozone (O3) is formed when ordinary oxygen molecules (O2) are split by ultraviolet radiation and then recombine with other oxygen molecules.
Crutzen showed in 1970 that the nitrogen oxides NO and NO2 react with ozone to hasten its destruction without being destroyed themselves. These nitrogen oxides occur when microorganisms in soil produce nitrous oxide (N2O).
Five years later, Molina and Rowland published a landmark article in Nature showing the threat to the ozone layer from chlorofluorocarbon (CFC) gases, which were being used widely in spray cans, refrigerators, and plastic foams. The two scientists realized that CFCs, which are chemically stable, could gradually be transported through normal air circulations to the stratosphere. There, intense ultraviolet light could break up the molecules, releasing chlorine, which catalyzes ozone destruction (just as nitrogen oxides do).
Although controversial at first, the Molina-Rowland hypothesis was strengthened in 1985 when a drastic seasonal depletion of stratospheric ozone over Antarctica--the "ozone hole"--was discovered. NCAR was a key player in subsequent experiments that brought research aircraft to the Antarctic and Arctic to further document polar ozone depletion and trace its causes. Smaller but still significant depletion has been found above the midlatitudes.
Why is the depletion so rapid and severe over the Antarctic? Crutzen and colleagues found that the chemical reactions were taking place on the surfaces of polar stratospheric clouds. These rare clouds are formed by water and nitric acid at extremely cold temperatures, primarily over Antarctica.
Through United Nations involvement, the Montreal Protocol on prohibition of CFC emissions was signed in 1987 and strengthened thereafter. With a few exceptions, the most dangerous gases will be completely banned by 1996. Still, the long lifetime of these gases means that damage to the ozone layer is likely to worsen for some years to come. Even if protocol guidelines are followed, it will take at least 100 years for the ozone layer to recover.
Only one other Nobel Prize has been awarded in the realm of atmospheric research (to Sir Edward Victor Appleton, 1947, in physics). "This is great recognition for atmospheric science as a whole," said Paul Sperry, ACD associate director. "It's also an example of basic research anticipating issues that are relevant to climate change and to society at large."
NCAR atmospheric chemist Jack Calvert, who has worked with all three Nobel winners, said, "I was impressed that they not only discovered [the ozone threat] but were willing to go to the government and say, 'We need to do something about this.' They're really heroes to us."
Writer: Bob Henson
Contact: Joan Vandiver Frisch
Manager, NCAR Media Relations
Boulder, Colorado 80307-3000
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