HFCs (hydrofluorocarbons), PFCs (perfluorocarbons), and SF6 (sulfur hexafluoride) are all extremely potent greenhouse trace gases. The reason for this is due to their very high Global Warming Potentials (GWPs). HFCs range from 140 times to 11,700 times more effective than carbon dioxide at trapping heat in the atmosphere. PFCs range from 650 times to 9,200 times more effective and SF6 is 23,900 times more effective. Thus, a very small increase in these trace gases can result in a huge amount of heat being absorbed. Not only do these gases enhance the greenhouse effect but they also have extremely long atmospheric lifetimes that contribute to the destruction of the stratospheric ozone layer.
HFCs and PFCs are synthetic chemicals that were introduced as an alternative to the stratospheric ozone destroying substances (ODSs) such as CFCs (chlorofluorocarbons). The Montreal Protocol of 1990 and the Copenhagen Amendments to the Montreal Protocol of 1992 called for a phase out of ODSs by 1996 for the United States. During the phase out period, HCFCs (hydrochlorofluorocarbons) were introduced, as they were deemed less harmful than CFCs. The HCFCs will eventually be phased out as well per the Montreal Protocol.
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Sources |
Emission Processes |
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Substitution of ODSs Class I: CFCs, CCl4, Halon
Class II: HCFCs |
Class I ODSs were used mainly for the purposes of refrigeration, air conditioning, foam blowing, cleaning solvent, dry cleaning, and fire extinguishers. Class II ODSs are interim replacements for the Class I products. They pose only 1/10 to 1/100 of the threat to stratospheric ozone as do the Class I gases. These too will be phased out. |
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HCFC-22 Production |
This is the main HCFC that is being produced as an interim substitute for CFCs |
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Electrical Transmission and Distribution |
Leaks of SF6 occur during the servicing of substations and circuit breakers. |
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Magnesium Production and Processing |
SF6 is used as a protective cover gas for the casting of molten magnesium. |
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Aluminum Production |
There are two different PFCs that are produced and emitted during the smelting process of aluminum. |
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Semiconductor Manufacture |
HFCs, PFCs and SF6 are used for plasma etching and chemical vapor deposition processes when semiconductors are manufactured. |
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