<P> At Montreal , the participants agreed to freeze production of CFCs at 1986 levels and to reduce production by 50 percent by 1999 . After a series of scientific expeditions to the Antarctic produced convincing evidence that the ozone hole was indeed caused by chlorine and bromine from manmade organohalogens , the Montreal Protocol was strengthened at a 1990 meeting in London . The participants agreed to phase out CFCs and halons entirely ( aside from a very small amount marked for certain `` essential '' uses , such as asthma inhalers ) by 2000 in non-Article 5 countries and by 2010 in Article 5 ( less developed ) signatories . At a 1992 meeting in Copenhagen , the phase - out date was moved up to 1996 . At the same meeting , methyl bromide ( MeBr ) , a fumigant used primarily in agricultural production , was added to the list of controlled substances . For all substances controlled under the protocol , phaseout schedules were delayed for less developed ( ' Article 5 ( 1 ) ' ) countries , and phaseout in these countries was supported by transfers of expertise , technology , and money from non-Article 5 ( 1 ) Parties to the Protocol . Additionally , exemptions from the agreed schedules could be applied for under the Essential Use Exemption ( EUE ) process for substances other than methyl bromide and under the Critical Use Exemption ( CUE ) process for methyl bromide . </P>
why the hole in the ozone layer over antarctica
chlorine bromine CFCs halons methyl bromide