Four chemicals said to be 'ecofriendly' are destroying the ozone layer
four chemicals that are thought to cause no damage to the ozone layer may be destroying the protective layer of the Earth, a new research suggests. The most harmful of the four is n-propyl bromide -- a solvent approved in 1997 by the us environmental protection agency (usepa) as a substitute for ozone-depleting substances such as chlorofluorocarbons (cfcs).
The chemical was known to be a potential ozone-destroyer. But it was assumed that it could not reach the ozone layer as it remains in the environment for less than 15 days. However, Donald Wuebbles of the University of Illinois, Urbana-Champaign, usa , and other experts have warned that when the chemical is released in the tropics, the weather systems there can send it into the stratosphere within days (www.newscientist.com,October 17, 2001). According to the researchers, even if the chemical breaks down in the lower atmosphere, it could still be churning out by-products that react with ozone-depleting bromine and help transfer it into the stratosphere. un scientists estimate that upto 10,000 tonnes of n-propyl bromide is manufactured each year and this figure is expected to rise up to 50,000 tonnes a year by 2010.
The other three harmful chemicals are hexachlorobutadiene, halon-1202 and 6-bromo-2-methoxy-naphthalene. Hexachlorobutadiene is a solvent and by-product of the manufacturing process of pvc . Tens of thousands of tonnes are manufactured each year. Halon-1202 is a chemical used in military aircraft and tanks, and 6-bromo-2-methoxy-naphthalene is put to use in the manufacture of the agricultural fumigant methyl bromide.
There is a growing fear among experts that there could be many other as-yet-unidentified ozone-destroying chemicals in widespread use. "Relatively small amounts of these new substances are being produced, but the levels of some of them are growing rapidly in the atmosphere," says John Pyle of the Centre for Atmospheric Science at the University of Cambridge, usa . "We cannot be complacent. If enough of these new chemicals are manufactured, we will delay the recovery of the ozone layer quite significantly," warns Mario Molina of the Massachusetts Institute of Technology, usa . n
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