The CFCs and HCFCs are wholly anthropogenic and do not exist naturally. They have been widely used as propellants in aerosols, as blowing agents in foam manufacture, in air conditioning units and refrigerants (CDIAC, 1991, 1993). The Montreal Protocol has recently cut emissions of many species by over 90%. Methylhalides are primarily produced in the oceans, usually associated with algal growth (Moore & Tokarczyk, 1993), although a significant fraction may come from biomass burning. Annual emissions of halocarbons may be found in IPCC (1995).