Report #: DOE/EIA-0573(2008)
• Greenhouse gases with high global warming potential (high-GWP gases) are hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), which together represented 2.5 percent of U.S. greenhouse gas emissions in 2008.
• Emissions estimates for the high-GWP gases are provided to EIA by the EPA’s Office of Air and Radiation. The estimates are derived from the EPA Vintaging Model.
• For this year’s EIA inventory, 2007 values for PFCs and SF6 are used as placeholders. The updated values will be available when the U.S. inventory is submitted to the UNFCCC in April 2010.
• Emissions of high-GWP gases have increased steadily since 1990 (Figure 25 on right and Table 26 below), largely because HFCs are being used to replace chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and other ozone-depleting substances that are being phased out under the terms of the Montreal Protocol, which entered into force on January 1, 1989.
• PFC emissions have declined since 1990 as a result of production declines in the U.S. aluminum industry as well as industry efforts to lower emissions per unit of output.
• HFCs are compounds that contain carbon, hydrogen, and fluorine. Although they do not destroy stratospheric ozone, they are powerful greenhouse gases.
• HFCs are used as solvents, residential and commercial refrigerants, firefighting agents, and propellants for aerosols.
• Emissions of substitutes for ozone-depleting substances, including HFC-32, HFC-125, HFC-134a, HFC-143a, and HFC-236fa, have grown from trace amounts in 1990 to nearly 121 MMTCO2e in 2008 (Table 27 below).
• Nearly 90 percent of the growth in HFC emissions since 1990 can be attributed to the use of HFCs as replacements for ozone-depleting substances. The market is expanding, with HFCs used in fire protection applications to replace Halon 1301 and Halon 1211.
• Since 2000, HFC-134a—used as a replacement for CFCs in air conditioners for passenger vehicles, trains, and buses—has accounted for the largest share of HFC emissions (Figure 26 on right).
• Under the Clean Air Act, manufacture and import of HCFC-22, except for use as a feedstock and in equipment manufacture before 2010, are scheduled to be phased out by January 1, 2010. Manufacturers of HCFC-22 are using cost-effective methods to make voluntary reductions in the amount of HFC-23 that is created as a byproduct of HCFC-22 manufacture; however, HCFC-22 production remains a large and steady source of U.S. emissions of HFC-23.
• Emissions of “other” HFCs, which are aggregated to protect confidential data, have been updated for 2008, showing a 4.4-percent increase from 2007.
• The two principal sources of PFC emissions are domestic aluminum production and semiconductor manufacture, which yield perfluoromethane (CF4) and perfluoroethane (C2F6) (Figure 27 on right and Table 28 below).
• While PFC emissions from aluminum production have declined markedly since 1990, the decline has been offset in part by increased emissions from semiconductor manufacturing.
• Emissions from process inefficiencies during aluminum production (known as “anode effects”) have been greatly reduced; in addition, high costs for alumina and energy have led to production cutbacks.
• Perfluoroethane is used as an etchant and cleaning agent in semiconductor manufacturing. The portion of the gas that does not react with the materials is emitted to the atmosphere.
• SF6, an excellent dielectric gas for high-voltage applications, is used primarily in electrical applications—as an insulator and arc interrupter for circuit breakers, switch gear, and other equipment in electricity transmission and distribution systems.
• Industry efforts to reduce emissions of SF6 from electrical power systems have led to a decline in emissions since 1990 (Figure 28 on right and Table 29 below).
• SF6 is also used in magnesium metal casting, as a cover gas during magnesium production, and as an atmospheric tracer for experimental purposes.
• Other, minor applications of SF6 include leak detection and the manufacture of loudspeakers and lasers.