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日期:2017-11-07 02:59:26 作者:司寇步 阅读:

By Ian Anderson in Melbourne A PREVIOUSLY ignored chemical is holding back the repair of the ozone layer. The amount of halon-1202 in the Earth’s atmosphere is now increasing by almost a fifth every year, say Australian and British researchers. Halons, which are widely used as fire retardants, contain bromine. Like chlorine, bromine destroys ozone in the upper atmosphere. The production and use of many halons is controlled under the Montreal Protocol, but the agreement says nothing about halon-1202. “The rapid growth of halon-1202 comes as a surprise,” says Paul Fraser of the Atmospheric Research Division of the CSIRO, Australia’s national research organisation, in Aspendale, Victoria. Fraser and his colleagues at the University of East Anglia in Norwich and ICI Chemicals and Polymers in Runcorn, Cheshire, have been analysing air collected over the past 20 years at Cape Grim on the northwest coast of Tasmania. Earlier this year, the team documented an alarming build-up of a hydrofluorocarbon with the potential to accelerate global warming (This Week, 7 February, p 13). The team’s latest analysis shows that bromine from all sources is increasing in the atmosphere by about 1.5 per cent per year. Halons, which contribute about 40 per cent of the total bromine, are increasing by about 3 per cent a year. Some increase in halons was expected. Western countries phased out the use of halons listed under the Montreal Protocol in 1994, apart from a few exempted applications, but developing countries do not have to do this until 2010. India, China and South Korea are major producers. At just 0.04 parts per trillion, the level of halon-1202 in the atmosphere is still much lower than that of other halons. But it is growing dramatically, reaching a rate of 17 per cent over each of the past two years (see Figure). Scientists hope that the ozone layer will begin to recover within the next two decades, but if the increase in halon-1202 continues unchecked, says Fraser, ozone levels may continue to fall. Exactly where the halon-1202 is coming from is a mystery. It could be a by-product of the manufacture of halon-1211, made in large quantities in China for portable fire extinguishers. Another possibility, raised in a paper that Fraser and his colleagues have submitted to the Journal of Geophysical Research, is that halon-1202 is being produced for firefighting on military aircraft and tanks. “There is one reference to this in the literature,” says Fraser,