A compound consisting of chlorine, fluorine, and carbon. CFCs are very stable in the troposphere. They move to the stratosphere and are broken down by strong ultraviolet (UV) light, where they release chlorine atoms that then deplete the ozone layer. CFCs are commonly used as refrigerants, solvents, and foam blowing agents. A table of all ozone-depleting substances shows their ODPs, global warming potentials (GWPs), and CAS numbers. CFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration (NOAA) provides more detailed information about CFCs on their web site (including graphs of their abundance in the atmosphere).
Class I Substance:
One of several groups of chemicals with an ozone-depletion potential of 0.2 or higher. Class I substances listed in the Clean Air Act (CAA) include CFCs, halons, carbon tetrachloride, and methyl chloroform. EPA later added HBFCs and methyl bromide to the list by regulation. A table of class I substances shows their lifetime ODPs, GWPs, and CAS numbers.
Class II Substance:
A chemical with an ozone-depletion potential of less than 0.2. Currently, all of the HCFCs are class II substances. Lists of class II substances with their ODPs, GWPs, and CAS numbers are available.
Clean Air Act (CAA):
Law amended by Congress in 1990. Title VI of the CAA directs EPA to protect the ozone layer through several regulatory and voluntary programs. Sections within Title VI cover production of ozone-depleting substances (ODS), the recycling and handling of ODS, the evaluation of substitutes, and efforts to educate the public.
Global Warming Potential (GWP):
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. A table of all ozone-depleting substances shows their ODPs, GWPs, and CAS numbers, and another table shows the GWPs for many non-ozone-depleting substances.
A compound consisting of hydrogen, chlorine, fluorine, and carbon. The HCFCs are one class of chemicals being used to replace the CFCs. They contain chlorine and thus deplete stratospheric ozone, but to a much lesser extent than CFCs. HCFCs have ozone depletion potentials (ODPs). Production of HCFCs with the highest ODPs are being phased out first, followed by other HCFCs. A table of ozone-depleting substances shows their ODPs, GWPs, and CAS numbers. HCFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration (NOAA) provides more detailed information about HCFCs on their website.
A compound consisting of hydrogen, fluorine, and carbon. The HFCs are a class of replacements for CFCs. Because they do not contain chlorine or bromine, they do not deplete the ozone layer. All HFCs have an ozone depletion potential of 0. Some HFCs have high GWPs. HFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration (NOAA) provides more detailed information about HFCs on its website.
The international treaty governing the protection of stratospheric ozone. The Montreal Protocol on Substances That Deplete the Ozone Layer and its amendments control the phaseout of ODS production and use. Under the Montreal Protocol, several international organizations report on the science of ozone depletion, implement projects to help move away from ODS, and provide a forum for policy discussions. In addition, the Multilateral Fund provides resources to developing nations to promote the transition to ozone-safe technologies. The full text of the Montreal Protocol is available from the United Nations Environmental Programme (UNEP).
A gas composed of three atoms of oxygen. Ozone is a bluish gas that is harmful to breathe. Nearly 90% of the Earth's ozone is in the stratosphere and is referred to as the ozone layer. Ozone absorbs a band of ultraviolet radiation called UVB that is particularly harmful to living organisms. The ozone layer prevents most UVB from reaching the ground.
Ozone-Depleting Substance(s) (ODS):
A compound that contributes to stratospheric ozone depletion. ODS include CFCs, HCFCs, halons, methyl bromide, carbon tetrachloride, 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 of class I and class II substances with their ODPs, GWPs, and CAS numbers are available.
Chemical destruction of the stratospheric ozone layer beyond natural reactions. Stratospheric ozone is constantly being created and destroyed through natural cycles. Various ozone-depleting substances (ODS), however, accelerate the destruction processes, resulting in lower than normal ozone levels. The science page offers much more detail on the science of ozone depletion.
Ozone Depletion Potential (ODP):
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 shows their ODPs, GWPs, and CAS numbers.
The region of the stratosphere containing the bulk of atmospheric ozone. The ozone layer lies approximately 15-40 kilometers (10-25 miles) above the Earth's surface, in the stratosphere. Depletion of this layer by ozone-depleting substances (ODS) will lead to higher UVB levels, which in turn will cause increased skin cancers and cataracts and potential damage to some marine organisms, plants, and plastics. The science page offers much more detail on the science of ozone depletion.
A refrigerant is one that was removed from refrigeration or air-conditioning equipment and stored in an external container without necessarily being tested or processed in any way.
A refrigerant is one that has been extracted and cleaned for reuse without meeting the stringent requirements for reclamation.
A refrigerant is one that has been reprocessed using specialized machinery and tested to meet industry purity standards.