Substances that have a positive ozone depletion potential (ODP) can thin the stratospheric ozone layer. Most of the ozone-depleting substances (ODS) are controlled by the United Nations Environment Programme (UNEP): The „Montreal Protocol on Substances that Deplete the Ozone Layer”. ODS include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, and methyl bromide. The most commonly used HCFCs today are HCFC-22 or R-22, which are still used in existing air conditioning and refrigeration equipment. Nevertheless, many ODSs are banned today and more are following.