NOBEL PRIZE TO OZONE RESEARCHERS
By Sean Henahan, Access Excellence
|Professor Paul Crutzen
||Professor Mario Molina
||Professor F. Sherwood Rowland|
Three noted chemistry researchers have been awarded the Nobel
Prize in Chemistry for atmospheric studies which led to an
understanding of how the ozone layer forms and decomposes. The
Royal Swedish Academy of Sciences praised the researchers'
contribution "to our salvation from a global environmental
problem that could have catastrophic consequences."
The one million dollar prize will be shared by F. Sherwood
Rowland, Bren Professor of Chemistry, UC Irvine; Mario Molina,
who currently is a member of the Department of Earth,
Atmospheric and Planetary Sciences at Massachusetts Institute
of Technology; and Paul Crutzen, a professor at Max-Planck
Institute for Chemistry in Germany and adjunct professor at
Scripps Institution of Oceanography at UC San Diego.
The award culminates 20 years of study on the ozone layer by the
researchers. The three winners of the Nobel Prize in Chemistry
are the first ever to receive the award for atmospheric
chemistry or environmental science.
Although the layer of ozone in the (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. The earth's stratosphere--the region 12
to 20 kilometers highearth contains small quantities of ozone a
gas with molecules consisting of three oxygen atoms. Ozone (O3)
is formed when ordinary oxygen molecules (O2) are split by
ultraviolet radiation and then recombine with other oxygen
molecules. If all the ozone in the atmosphere were compressed to
a pressure corresponding to that at the earth's surface, the
layer would be only 3 mm thick. But even though ozone occurs in
such small quantities, it plays an exceptionally fundamental
part in life on earth.
This is because ozone, together with ordinary molecular oxygen,
is able to absorb the major part of the sun's ultra-violet
radiation and therefore prevent this dangerous radiation from
reaching the surface. Without a protective ozone layer in the
atmosphere, animals and plants could not exist, at least upon
land. The new Nobel recipients research revealed much about the
processes that regulate the atmosphere's ozone content.
In 1970, Dr. Crutzen showed 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, Drs. 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 circulation to
the stratosphere. There, intense ultraviolet light could break
up the molecules, releasing chlorine, which catalyzes ozone
destruction (just as nitrogen oxides do).
Molina and Rowlands' hypotheses was highly controversial when
first proposed and brought a storm of protest from industrial
producers of ozone. However, the researchers gained considerable
support in 1985 when a drastic seasonal depletion of
stratospheric ozone over Antarctica--the "ozone hole"--was
Satellite view of ozone hole (NASA)
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
However, in a recent development, the Republicans in the US
Congress have introduced legislation to overturn U.S.
participation in the international ban on the production of
chlorofluorocarbons, or CFCs.
In 1930 the English physicist Sidney Chapman formulated the
first photochemical theory for the formation and decomposition
of ozone in the atmosphere. This theory, which describes how
sunlight converts the various forms of oxygen from one to
another, explains why the highest contents of ozone occur in the
layer between 15 and 50 km, termed the ozone layer. Later
measurements, however, showed appreciable deviations from
Chapman's theory. The calculated ozone contents were
considerably higher than the observed ones. This led scientists
to look for other chemical reactions contributing to the
reduction of the ozone content. Some years later the Belgian
Marcel Nicolet contributed important knowledge of how the
decomposition of ozone was enhanced by the presence of the
hydrogen radicals OH and HO
The power of nitrogen oxides to decompose ozone was noted by the
American researcher Harold Johnston, who carried out extensive
laboratory studies of the chemistry of nitrogen compounds. In
1971 he pointed out the possible threat to the ozone layer that
the planned fleet of supersonic aircraft and supersonic travel
(SST) might represent. These aircraft would be capable of
releasing nitrogen oxides right in the middle of the ozone layer
at altitudes of 20 km. Crutzen's and Johnston's work gave rise
to a very intensive debate among researchers as well as among
technologists and decision-makers.
The next important development in ozone chemistry came in 1974,
when Molina and Rowland published their widely noted Nature
article on the threat to the ozone layer from chlorofluorocarbon
(CFC) gases - "freons" - used in spray bottles, as the cooling
medium in refrigerators and elsewhere and plastic foams.
Molina and Rowland based their conclusions on two important
contributions by other researchers. James Lovelock had recently
developed a highly sensitive device of measuring extremely low
organic gas contents in the atmosphere, the electron capture
detector. Using this he could now demonstrate that the
exclusively man-made, chemically inert, CFC gases had already
spread globally throughout the atmosphere. Richard Stolarski and
Ralph Cicerone had shown that free chlorine atoms in the
atmosphere can decompose ozone catalytically in similar ways as
nitrogen oxides do.
The ozone controversy raises the issue of how mankind is
affecting the climate. Ozone, like carbon dioxide and methane,
is a greenhouse gas that contributes to high temperatures at the
surface of the earth. (CFC gases have a similar effect). Model
calculations have shown that the climate is specially sensitive
to changes in the ozone content in the lower layers, the
troposphere. Here the ozone content has increased markedly
during the past century, chiefly because of the release of
nitric oxide, carbon monoxide and gaseous hydrocarbons from
vehicles and industrial processes and from the combustion of
biomass in the tropics. The elevated ozone content in lower
atmospheric layers is itself an environmental problem for the
damage it can cause to crops and human health.
Thanks to the Royal Swedish Academy of Sciences for providing
resources used in the
preparation of this article.
Graedel, T. E. and Crutzen, P.J., Atmosphere, climate and
change. Scientific American Library, 1995.
Rowland, F. S. and Molina, M. J., Ozone depletion: 20 years
after the alarm, Chemical and Engineering News 72, 8-13, 1994
Scientific assessment of ozone depletion 1994, WMO Report 37,
World Meteorological Organization and United Nations Environment
Programme, Geneva, 1995.
Toon, O. B. and Turco, R. P., Polar stratospheric clouds and
ozone depletion, Scientific American 264, 68-74, 1991.
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