TWO decades ago, most scientists would have scoffed at the idea that industrial gases could destroy ozone high up in the stratosphere. Last week, however, three men who showed that this notion is more than just hot air received the Nobel Prize for Chemistry.
Paul Crutzen of the Max Planck Institute for Chemistry in Mainz, Mario Molina of the Massachusetts Institute of Technology and Sherwood Rowland of the University of California at Irvine explained the chemical reactions that are destroying the ozone layer. They played a key role in solving 鈥渁 global environmental problem that could have catastrophic consequences鈥�, reads the citation from the Royal Swedish Academy of Sciences. 鈥淭hey鈥檝e done superb science,鈥� agrees Dudley Herschbach of Harvard University, who received the chemistry Nobel in 1986. 鈥淚 don鈥檛 think anyone thought of environmental problems in that broad perspective before.鈥�
While working at Stockholm University in 1970, Crutzen, a Dutch-born meteorologist, discovered that the nitrogen oxides NO and NO2 catalyse the breakdown of stratospheric ozone into molecular oxygen. These gases are produced in the atmosphere from nitrous oxide (N2O), which is released by microorganisms in soil. Crutzen showed that this is the main pathway for breaking down ozone naturally.
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His work led Harold Johnston, an atmospheric chemist at the University of California at Berkeley, to realise that supersonic aircraft would destroy stratospheric ozone by releasing nitrogen oxides smack in the middle of the ozone layer.
Rowland and Molina built on this work. Rowland鈥檚 life took a critical turn after hearing a talk by the English scientist James Lovelock in 1972. Lovelock had invented a device called an electron capture detector, with which he had measured trace levels of CFCs in the atmosphere.
Rowland was intrigued by the fate of these CFCs. So was Molina, who joined Rowland at Irvine in 1973. Around Christmas that year, the pair visited Johnston, who told them about new findings which showed that free chlorine atoms catalyse ozone breakdown.
Rowland and Molina completed the jigsaw: CFCs would diffuse into the upper atmosphere, where the Sun鈥檚 ultraviolet light would break them down, liberating chlorine. In 1974, they predicted that this could reduce stratospheric ozone levels by several per cent.
Despite initial scepticism, further studies only confirmed Molina and Rowland鈥檚 work, and led to CFCs being banned as aerosol propellants. Ironically, Molina and Rowland underestimated the problem. They did not predict the ozone hole which Joe Farman of the British Antarctic Survey discovered in 1985. 鈥淭he hole woke everyone up, and made them realise action was required in 10 years, not 100,鈥� says Farman. In 1987, the Montreal Protocol laid down a schedule for phasing out CFC production.
Crutzen was on holiday last week in Spain. Molina, flanked by his wife and collaborator, Luisa, told a press conference at MIT: 鈥淚t was a big surprise, a very pleasant surprise.鈥� Molina is the first Mexican to receive a scientific Nobel.
Rowland, meanwhile, confessed to a feeling of 鈥渘umbness鈥� when he received a call at 6.30 in the morning from the Swedish academy. 鈥淭he Nobel prize tells you that the scientific community thinks this is one of the more important 鈥� discoveries of recent times,鈥� he says.
Less pleased by the Nobel award is the very small group of diehards who deny that CFCs are destroying the ozone layer. One prominent sceptic, Fred Singer, president of the Science and Environmental Policy Project in Fairfax, Virginia, told New 杏吧原创: 鈥淭he Swedish academy has chosen to make a political statement.鈥�