Rebuilding the Ozone Layer

摘要

This year's International Ozone Day - Sept.16,2007 - marked the 20th anniversary of the signing of the Montreal Protocol,which required countries to phase out production and use of compounds that deplete ozone in the stratosphere.Such substances include chlorofluorocarbons(CFCs),halons,carbon tetrachloride and methyl chloroform.Initially signed by 24 countries in 1987,this treaty today covers 191 countries.