Temps de lecture :2 minutes
Reaction data of crucial chloride compounds called into question.
As the world marks 20 years since the introduction of the Montreal Protocol to protect the ozone layer, Nature has learned of experimental data that threaten to shatter established theories of ozone chemistry. If the data are right, scientists will have to rethink their understanding of how ozone holes are formed and how that relates to climate change. […]
So Markus Rex, an atmosphere scientist at the Alfred Wegener Institute of Polar and Marine Research in Potsdam, Germany, did a double-take when he saw new data for the break-down rate of a crucial molecule, dichloride peroxide (Cl2O2). The rate of photolysis (light-activated splitting) of this molecule reported by chemists at NASA’s Jet Propulsion Laboratory in Pasadena, California, was extremely low in the wavelengths available in the stratosphere — almost an order of magnitude lower than the currently accepted rate. “This must have far-reaching consequences,” Rex says. “If the measurements are correct we can basically no longer say we understand how ozone holes come into being.” […]
The rapid photolysis of Cl2O2 is a key reaction in the chemical model of ozone destruction developed 20 years ago. If the rate is substantially lower than previously thought, then it would not be possible to create enough aggressive chlorine radicals to explain the observed ozone losses at high latitudes, says Rex. The extent of the discrepancy became apparent only when he incorporated the new photolysis rate into a chemical model of ozone depletion. The result was a shock: at least 60% of ozone destruction at the poles seems to be due to an unknown mechanism, Rex told a meeting of stratosphere researchers in Bremen, Germany, last week. [this article was published on 27. September 2007]
“Our understanding of chloride chemistry has really been blown apart,” says John Crowley, an ozone researcher at the Max Planck Institute of Chemistry in Mainz, Germany.[…]
“Reactions in experimental chambers are one thing — the free atmosphere is something else,” says Joe Farman, one of the scientists who first quantified the ozone hole over Antarctica. “There’s no doubt that ozone disappears at up to 3% a day — whether or not we completely understand the chemistry.” But he adds that insufficient control of substances such as halon 1301, used as a flame suppressor, and HCFC22, a refrigerant, is a bigger threat to the success of the Montreal Protocol than are models that don’t match the observed losses. […]
Reprinted by permission from Macmillan Publishers Ltd: Nature 449, 382-383, copyright 2007