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Frank Sherwood Rowland

(b. 1927)


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Mario Molina (b. 1943) Mexican chemist

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(1927–) American chemist

Born in Delaware, Ohio, Rowland was educated at Wesleyan University, Ohio, and at the University of Chicago, where he gained his PhD in 1952. After holding teaching posts at Princeton and Kansas, Rowland moved to the University of California, Irvine, in 1964 as professor of chemistry.

Shortly before Christmas 1973, Mario Molina took to Rowland, his postdoctoral adviser, some calculations suggesting that CFCs (chlorofluorocarbons), widely used in aerosol propellants, will rise to the upper atmosphere and destroy the ozone layer, located 8 to 30 miles above the Earth. As the layer protects us from harmful ultraviolet rays, its destruction could have disturbing consequences.

Rowland and Molina published their preliminary results in June 1974. They pointed out that in the lower atmosphere CFCs were relatively inert compounds. But at a height of about 25 kilometers in the stratosphere they begin to absorb ultraviolet radiation in the 1900–2250 angstrom range and decompose, releasing chlorine atoms which will attack ozone (O3) atoms in a chain reaction:

Cl∙ + O3 → ClO + O2

ClO + O∙ → Cl∙ + O2

In the first part of the reaction a chlorine atom attacks an ozone molecule and forms chlorine monoxide and normal oxygen; in the second stage of the reaction, involving oxygen atoms, the chlorine is regenerated and is free to enter once more into the first reaction, destroying an ozone molecule in the process. The result is that a relatively small amount of CFC can destroy a large amount of ozone.

Rowland discovered that 400,000 tons of CFCs had been produced in the United States in 1973, and that the bulk of this was being discharged into the atmosphere. He calculated that at the then current production rate there would be a long-term steady-state ozone depletion of 7–13%. The CFC industry responded by pointing out there was no actual proof of Rowland's hypothesis. Further, they argued, even if the hypothesis was true, other atmospheric processes could offset the effects of the reaction. In 1974 it seemed that Rowland had found just such a process with the possible formation of chlorine nitrate (ClONO2) in the atmosphere. Thus it seemed possible that the reaction:

ClO + NO2 → ClONO2

would remove chlorine monoxide, leaving less chlorine to react with ozone. More detailed analysis revealed that chlorine nitrate might change the distribution of ozone in the atmosphere without significantly minimizing its depletion rate. The National Academy of Sciences published a report in September 1976 supporting the work of Rowland and Molina, and in October 1978 CFC use in aerosols was banned in the United States. Final confirmation came when Joe Farman discovered in late 1984 a 40% ozone loss over Antarctica.

For his work on CFCs Rowland shared the 1995 Nobel Prize for chemistry with Mario Molina and Paul Crutzen.

Subjects: Science and Mathematics.


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