Phaseout of Class I Ozone-Depleting Substances
In the United States, “Class I” ozone-depleting substances (ODSA compound that contributes to stratospheric ozone depletion. ODS include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform. ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down, they release chlorine or bromine atoms, which then deplete ozone. A detailed list (http://www.epa.gov/ozone/science/ods/index.html) of class I and class II substances with their ODPs, GWPs, and CAS numbers are available.) were subject to the first round of phaseout targets under the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol). Class I ODS have an ozone depletion potentialA number that refers to the amount of ozone depletion caused by a substance. The ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11. Thus, the ODP of CFC-11 is defined to be 1.0. Other CFCs and HCFCs have ODPs that range from 0.01 to 1.0. The halons have ODPs ranging up to 10. Carbon tetrachloride has an ODP of 1.2, and methyl chloroform's ODP is 0.11. HFCs have zero ODP because they do not contain chlorine. A table of all ozone-depleting substances (http://www.epa.gov/ozone/science/ods/index.html) shows their ODPs, GWPs, and CAS numbers. of 0.2 or higher, and include halons, chlorofluorocarbonsGases covered under the 1987 Montreal Protocol and used for refrigeration, air conditioning, packaging, insulation, solvents, or aerosol propellants. Since they are not destroyed in the lower atmosphere, CFCs drift into the upper atmosphere where, given suitable conditions, they break down ozone. These gases are being replaced by other compounds: hydrochlorofluorocarbons, an interim replacement for CFCs that are also covered under the Montreal Protocol, and hydrofluorocarbons, which are covered under the Kyoto Protocol. All these substances are also greenhouse gases. See hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, ozone depleting substance. (CFCs), methyl chloroformA compound consisting of carbon, hydrogen, and chlorine. Methyl chloroform is used as an industrial solvent. Its ozone depletion potential is 0.11., carbon tetrachlorideA compound consisting of one carbon atom and four chlorine atoms. Carbon tetrachloride was widely used as a raw material in many industrial uses, including the production of chlorofluorocarbons (CFCs), and as a solvent. Solvent use ended when it was discovered to be carcinogenic. It is also used as a catalyst to deliver chlorine ions to certain processes. Its ozone depletion potential is 1.2., and methyl bromideA compound consisting of carbon, hydrogen, and bromine. Methyl Bromide is an effective pesticide used to fumigate soil and many agricultural products. Because it contains bromine, it depletes stratospheric ozone and has an ozone depletion potential of 0.6. Production of methyl bromide was phased out on December 31, 2004, except for allowable exemptions. Much more information is available (http://www.epa.gov/ozone/mbr/index.html).. Class II ODS are subject to a different phaseout schedule.
Section 604 of the Clean Air Act establishes the phaseout targets for Class I ODS. The ban on production and import of halons took effect on January 1, 1994. The ban on production and import of other Class I ODS—excluding methyl bromide—took effect on January 1, 1996. There are several exemptions from the phaseout.
Learn more information about the phaseout of Class I substances in this fact sheet.
|CFCs||Halons||Carbon Tetrachloride||Methyl Chloroform||Methyl Bromide||Hydrobromofluorocarbons|