(B) The Montreal Protocol on Substances that Deplete the Ozone Layer is an international treaty designed to protect the ozone layer from chlorofluorocarbon by phasing out the production of numerous substances that are responsible for ozone depletion. The treaty is structured around several groups of halogenated hydrocarbons that deplete stratospheric ozone. All of the oz one-depleting substances controlled by the Montreal Protocol contain either chlorine or bromine (substances containing only fluorine do not harm the ozone layer).