Ozone-Depleting Substances

This page provides information on compounds recognized as ozone-depleting substances ( ODS A 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. ) under the Montreal Protocol.

The ODS are split into two groups under the Clean Air Act: Class I ODS, such as chlorofluorocarbons Gases 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), and Class II ODS, such as hydrochlorofluorocarbons Compounds containing hydrogen, fluorine, chlorine, and carbon atoms. Although ozone depleting substances, they are less potent at destroying stratospheric ozone than chlorofluorocarbons (CFCs). They have been introduced as temporary replacements for CFCs and are also greenhouse gases. See ozone depleting substance. (HCFCs).

For each ODS, this page provides the compound’s atmospheric lifetime, Ozone Depletion Potential A 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. (ODP), Global Warming Potential A number that refers to the amount of global warming caused by a substance. The GWP is the ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. Thus, the GWP of CO2 is defined to be 1.0 . CFC-12 has a GWP of 8,500, while CFC-11 has a GWP of 5,000. Various HCFCs and HFCs have GWPs ranging from 93 to 12,100. Water, a substitute in numerous end-uses, has a GWP of 0. A table of all ozone-depleting substances (http://www.epa.gov/ozone/science/ods/index.html) shows their ODPs, GWPs, and CAS numbers, and another table shows the GWPs for many non-ozone-depleting substances (http://www.epa.gov/ozone/geninfo/gwps.html). (GWP), and Chemistry Abstract Service (CAS) registry numbers.

Information on acceptable ODS alternatives (e.g., hydrofluorocarbons) is available through EPA’s Significant New Alternatives Policy (SNAP) Program.

Class I ODS

Class I ODS are divided into eight groups.

• Class I ODS listed in Groups 1 through 5 are identified in Title VI of the Clean Air Act.
• Class I ODS listed in Groups 6 and 7, methyl bromide and hydrobromofluorocarbons, are identified in EPA's Accelerated Phaseout final rule.
• Class I ODS listed in Group 8, chlorobromomethane, is identified in EPA's Chlorobromomethane Phaseout final rule.

Why are there multiple values given for the ODPs and GWPs?

The numbers in the “ODP1” column are from the Montreal Protocol. Some numbers have been updated as per amendments to the Protocol.

Data in the “ODP2” column come from WMO’s Scientific Assessment of Ozone Depletion: 2010. 1 ODP values listed are semi-empirical and can be found in Table 5-1 of the document.

The numbers in the “GWP1” column represent global warming potentials over a 100-year time horizon. The numbers are from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report: Climate Change 2007 (AR4). 2 The values listed are for direct radiative forcing and can be found in Table 2.14 of the “Physical Science Basis” contribution to the report.

The numbers in the “GWP2” column also represent global warming potentials over a 100-year time horizon. The numbers are from the IPCC Fifth Assessment Report: Climate Change 2014 (AR5). The values listed are for direct radiative forcing and can be found in Table 8.A.1 of the “Physical Science Basis” contribution to the report. 3

References

1. WMO (World Meteorological Organization), 2011: Scientific Assessment of Ozone Depletion: 2010. Global Ozone Research and Monitoring Project—Report No. 52, Geneva, Switzerland, 516 pp.
2. IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.
3. IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.

Class II ODS

Why are there multiple values given for the ODPs and GWPs?

The numbers in the “ODP1” column are from the Montreal Protocol. Some numbers have been updated as per amendments to the Protocol.

Data in the “ODP2” column come from WMO’s Scientific Assessment of Ozone Depletion: 2010. 1 ODP values listed are semi-empirical and can be found in Table 5-1 of the document.

The numbers in the “GWP1” column represent global warming potentials over a 100-year time horizon. The numbers are from the IPCC Fourth Assessment Report: Climate Change 2007 (AR4). 2 The values listed are for direct radiative forcing and can be found in Table 2.14 of the “Physical Science Basis” contribution to the report.

The numbers in the “GWP2” column also represent global warming potentials over a 100-year time horizon. The numbers are from the IPCC Fifth Assessment Report: Climate Change 2014 (AR5). The values listed are for direct radiative forcing and can be found in Table 8.A.1 of the “Physical Science Basis: contribution to the report. 3

References

1. WMO (World Meteorological Organization), 2011: Scientific Assessment of Ozone Depletion: 2010. Global Ozone Research and Monitoring Project—Report No. 52, Geneva, Switzerland, 516 pp.
2. IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.
3. IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.

• Background and Science
  • Basic Ozone Layer Science
  • Health and Environmental Effects of Ozone Layer Depletion
  • Ozone-Depleting Substances
  • Current State of the Ozone Layer
  • Atmospheric and Health Effects Framework Model
  • EPA’s Vintaging Model of ODS Substitutes