Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 1999, 38 (16), 2408 - 2410
News from the Ozone Hole
Italian chemists examine formerly unknown
but possibly important reactions
in the ozone layer
The chemical reactions that lead to the formation of the ozone hole in the upper layers of the atmosphere have not yet all been understood. Chemists continue to find new threads in the tangled web of conversions involving trace atmospheric substances such as chlorofluorocarbons (CFCs) and gases such as ozone and oxygen. An Italian research group working with Giulia de Petris at "La Sapienza" University of Rome have now examined the reactions between CFCs and electrically charged atmospheric molecules - these particles apparently play a more important role than was formerly assumed.
Mass spectrometers are very successful at detecting trace molecules in the atmosphere. These instruments, which identify molecules by their mass, do so with a sensitivity that would allow them to recognize a single hair among the hair of all of the people on earth. Since it is possible to mount mass spectrometers on rockets, it is known that atmospheric molecules, becoming electrically charged through the influence of ionizing cosmic radiation, play an important role in complex atmospheric chemistry. They can limit the lifetime of harmful molecules.
What is formed in these reactions between CFCs and the charged particles has not previously been determined. De Petris and his co-workers have now addressed this question - also with a mass spectrometer. As a typical example of a chlorofluorocarbon, they examined dichlorofluoromethane (R21 or Halon 1120) in a mixture of electrically charged ozone and oxygen gases. The result: the ozone transferred its charge to the CFC molecule and formed a weak chemical bond with this newly formed ion. The product of this reaction then decomposed to form carbon monoxide and another charged molecule. The ozone was destroyed by this reaction. These results were so unexpected that the chemists didn't believe them until they had been confirmed with extensive computer calculations.
These discoveries will certainly not make the ozone hole any larger than it already is, but atmospheric scientists will be able to use de Petris' results to refine their computer models even further.