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Scientists warn of perils posed by substitutes for CFCs

作者:杜榕瀹    发布时间:2019-02-26 09:10:11    

BRITISH scientists assessing damage to the ozone layer warned last week that undue reliance on hydrochloro fluorocarbons (HCFCs), the first generation of substitutes for chlorofluorocarbons which damage ozone, may compound the problems posed by existing CFCs and other ozone-depleting chemicals called halons. This warning comes in the latest report of the UK Stratospheric Review Group, published last week. The group, chaired by John Pyle, a distinguished atmospheric chemist from the University of Cambridge, is critical of the scientific foundation on which the present control regime is based. The Montreal Protocol relies on the concept of ozone depletion potential (ODP) to com pare the impact of different compounds on the stratospheric ozone layer. Under this approach, compounds such as CFC substitutes, which have a less damaging effect on ozone than the original CFCs, appear to be less of a threat. The report suggests that this conclusion is misleading. The working group argues strongly that what is important at any one time is the amount of chlorine in the atmosphere, not the lifetime of the individual compounds involved. ‘The use of ODP is limited by the failure of models to predict ozone depletion correctly and by the fact that it refers to steady-state conditions which preclude predictions of changes over the next few decades,’ says the report. The group points out that the amount of airborne chlorine has doubled since 1973. Under the existing terms of the Montreal Protocol, the rise will continue throughout the next century. The scientists say that priority should be given to halting this rise. They suggest that chlorine concentrations should be pegged at between 1.5 and 2 parts per billion in air, the concentration before the ozone hole appeared. Initially, the target should be to hold the peak loading of chlorine at 4 ppb. At present the concentration of chlorine in the stratosphere is about 3 ppb. This will inevitably rise as chlorine in the lower atmosphere, the troposphere, reaches the stratosphere over the next few years. ‘Substitution of CFCs by HCFCs in other than modest proportion, depending on the lifetime of the particular HCFC used, could both increase the peak chlo rine loading and sustain unprecedented levels of stratospheric chlorine,

 

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