Refrigerants make air conditioning and refrigeration possible, which contribute enormously to our quality of life. In this equipment, refrigerants are the working fluid used to absorb and transfer heat from one part of the air conditioning or refrigeration system to another.

But in recent decades, it was found that, when released into the atmosphere, refrigerants containing chlorine — chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) — could damage the Earth’s protective ozone layer. In addition, most also enhance the greenhouse effect, leading to accelerated global warming.

In 1987, an international environmental agreement known as the Montreal Protocol on Substances that Deplete the Ozone Layer established requirements that began the worldwide phaseout of CFC and HCFC compounds. In response to this agreement, the United States amended the Clean Air Act, adding provisions to establish a schedule to phaseout the use of CFC and HCFC compounds.

The phaseout is set over a 40-year period that began in 1995, and schedules for refrigerants vary by how harmful it is to the Earth’s ozone layer. Each chemical compound identified in the Montreal Protocol as an ozone-depleting substance also is categorized by its ozone-depleting potential (ODP) and its global warming potential (GWP). The higher the number, the more potentially damaging the substance is to our environment. A table of all ozone-depleting substances shows their ODPs, GWPs, and CAS numbers.

The phaseout has operated by reducing in stages the amount of ozone-depleting substances that may be legally produced or imported into the U.S. CFCs were the first refrigerant on the schedule to be phased out because they have ozone depleting potential.