By Fred Pearce
The healing of the ozone layer could be delayed for 30 years or more by rising emissions of a substance hitherto ignored by environmental regulators. Ironically, its principal use is as a feedstock to make “ozone-friendly” chemicals for air conditioners and refrigerators.
As emissions of CFCs and other ozone-eating chlorine compounds are curbed under the 30-year-old Montreal Protocol, emissions of another chemical called dichloromethane – also known as methylene chloride – have been rising, says Ryan Hossaini of Lancaster University, UK. They now total over a million tonnes a year, and concentrations of dichloromethane in the lower atmosphere have doubled since 2004.
The chemical, a volatile gas, has many uses, including as an industrial solvent and paint remover. The recent growth in its emissions – stemming either from production leaks or deliberate venting – are particularly tied to its increasing role in the manufacture of a hydrofluorocarbon called HFC-32, a widely used replacement for CFCs.
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