Emissions of Greenhouse Gases in the United States 2000
Other Gases: Hydrofluorocarbons, Perfluorocarbons, and Sulfur Hexafluoride
Hydrofluorocarbons (HFCs) | Perfluorocarbos (PFCs) | Sulfur Hexafluoride (SF6) | Ozone-Depleting Substances and Criteria Pollutants
Overview
In
addition to the three principal gases (carbon dioxide, methane, and nitrous
oxide), there are other gases that account for 2.5 percent of U.S. greenhouse
gas emissions when weighted by global warming potential (GWP) (see
discussion on "IPCC Calculates New Global Warming Potentials in 2001").
These gases are engineered chemicals that occur on a very limited basis in
nature.75 Although they are more potent
greenhouse gases and tend to have comparatively high GWPs, they are emitted
in such small quantities that their overall impact is currently small.
The guidelines of the Intergovernmental Panel on Climate Change (IPCC) define three classes of these gases that “count” for emissions estimation: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). This chapter describes emissions sources and gives emissions estimates for HFCs, PFCs, and SF6.
HFCs, PFCs, and SF6 are emitted in small quantities, but they have disproportionate effects because of their large GWPs. PFCs and SF6 have particularly high GWPs because of their scarcity in the atmosphere and long atmospheric lifetimes. SF6 is the most potent of the greenhouse gases, with a GWP of 22,200. PFCs have GWPs in the range of 7,000 to 9,000. HFC-23 is the most potent of the HFCs, with a GWP of 12,000.76
Table 29 summarizes U.S. emissions of HFCs, PFCs, and SF6 from 1990 to 2000, and Table 30 shows the corresponding emissions in million metric tons carbon equivalent. The U.S. Environmental Protection Agency (EPA) estimates total emissions of HFCs, PFCs, and SF6 in 2000 at 46.8 million metric tons carbon equivalent—a 4.5-percent increase over 1999 emissions and a 57.8-percent increase over 1990 emissions.77
In summary, emissions of HFCs and PFCs are rising, and new data for SF6 show a decline. In the case of HFCs, the rise in emissions reflects the use of HFCs as replacements for CFCs, whose use is being phased out under the Montreal Protocol because they damage the Earth’s ozone layer. CFCs had been widely used as refrigerants, aerosol propellants, and foam blowing agents for many years, but with CFC production virtually ceasing by 1996, HFCs have been introduced into the market to fill the void in many key applications. The trend in HFC emissions is expected to accelerate in the next decade as HCFCs used as interim substitutes for CFCs are also phased out under the provisions of the Copenhagen Amendments to the Montreal Protocol.
Emissions of PFCs and perfluoropolyethers (PFPEs) have also been rising since 1990 (although not as rapidly as HFC emissions), mainly because of the recent commercial introduction of new PFCs and PFPEs both as CFC substitutes and for use in various applications in the semiconductor manufacturing industry. New data for SF6 show an overall decline in emissions, 41.4 percent since 1990, as opposed to previous years’ estimations. The change is the result of lower estimates of emissions from electrical transmissions and distribution.78
The emissions estimates in Table 29 are taken from data supplied by the EPA’s Office of Air and Radiation.79 The estimates in Table 30 are based on data provided by the EPA’s Office of Air and Radiation in units of native gas, which were converted to carbon-equivalent units by EIA, using GWP values from the IPCC’s 2001 Third Assessment Report (see discussion onn "IPP Calculates New Global Warming Potentials in 2001"). The 2000 preliminary estimates are advance estimates developed by the EPA and provided to EIA. They include some relatively minor revisions to the historical emissions estimates for HFCs, based on recent runs of the EPA’s Vintaging Model, as well as significant revisions to historical emissions estimates for SF6 based on new data for SF6 emissions from electrical equipment (see discussions on" EPA Revises Emissions Estimation Methodology" and "The EPA Vintaging Model: Estimation Methods and Uncertainty"). The revisions to the historical estimates are reflected in the emissions estimates presented in this chapter.
Hydrofluorocarbons (HFCs)
HFCs are compounds containing carbon, hydrogen, and fluorine. They do not destroy ozone. The market for HFCs is expanding as CFCs are being phased out. Since 1990, HFC emissions have accounted for a growing share (almost 70 percent in 2000) of total carbon-equivalent emissions of HFCs, PFCs, and SF6 combined. The EPA estimates U.S. emissions of all HFCs in 2000 at 28.1 million metric tons carbon equivalent, an 8.3-percent increase from 1999 emissions and a 181.4-percent increase from 1990.80
Trifluoromethane (HFC-23)
Although emissions of HFC-23 are relatively small, its high GWP (12,000)81 gives it a substantial direct effect. HFC-23 is created as a byproduct in the production of HCFC-22 and is generally vented to the atmosphere.
The EPA estimates 2000 HFC-23 emissions at 2,546 metric tons of gas.82 Annual emissions have fluctuated since 1990, reaching a low point in 1995 at 2,310 metric tons and peaking at 3,432 metric tons in 1998 (Table 29). The estimate for 2000 is 15 percent lower than the estimate of 1990 emissions. Consumption of HCFC-22 continues to grow, although at a slower rate than in past years. It continues to dominate the refrigerant market for stationary refrigeration and air conditioning (including chillers,
room air conditioners, and dehumidifiers).83 In addition, HCFC-22 is manufactured as a feedstock for production of polytetrafluoroethylene (PTFE) and other chemicals. The EPA administers a voluntary program with HCFC-22 producers to reduce HFC-23 emissions, which may help to offset the rising demand for HCFC-22 in the short term. In the long term, domestic production of HCFC-22 for use as a refrigerant will be phased out by 2010 under the U.S. Clean Air Act, pursuant to U.S. agreements under the Copenhagen Amendments to the Montreal Protocol, although its production for use as a feedstock will be allowed to continue indefinitely.84
1,2,2,2-Tetrafluoroethane (HFC-134a)
HFC-134a, with a GWP of 1,300,85 has been the industry standard for replacing CFCs in automotive air conditioners since 1994. Emissions in 1990 were estimated at 562 metric tons of gas, but since then they have grown rapidly to 33,669 metric tons in 2000 (Table 29). The 2000 estimate is 10.8 percent higher than that for 1999.
Automobile air conditioners are subject to leakage, with sufficient refrigerant leaking (15 to 30 percent of the charge) over a 5-year period to require servicing. On its Form EIA-1605, General Motors (GM) reported total HFC-134a emissions of about 2,566 metric tons of gas in 1999.86 GM based its estimate on an assumed annual leakage rate from mobile sources of 10 percent per year. With GM vehicles accounting for about one-third of the U.S. light-duty fleet,87 the GM emissions estimate implies that total U.S. HFC-134a emissions from mobile air conditioners were equal to about 7,700 metric tons in 1999. Emissions from this source are expected to continue to increase in the near future, as the replacement of vehicles using CFCs proceeds at a rapid pace.
In addition to its use in all new automobiles, an automotive aftermarket for HFC-134a has been developing. Spurred by rising prices for CFC-12, 5 million cars were retrofitted for HFC-134a use in 1997.88 This trend toward retrofitting is expected to continue, given that CFC-12 is no longer produced, remaining inventories are being depleted, and CFC-12 prices are rising.89 Furthermore, many of the air conditioners in mid-1990s models (which were among the first automobiles to use HFC-134a) are now due to be serviced. In 1999, a spokesperson for Elf Atochem North America estimated the U.S. aftermarket for HFC-134a at 45 to 50 million pounds, or roughly 35 percent of total annual demand. He believed that, as the market for HFC-134a matures, the aftermarket will eventually be about twice the size of the original equipment market.90 The automotive aftermarket is already responsible for much of the growth in current HFC-134a demand.91
HFC-134a is also used in refrigerant blends (e.g. R-404) in most new refrigerators built in the U. S. and in commercial chillers, but leakage from these sources is much less than from automotive air conditioners. Leakage occurs primarily during servicing of the units rather than during normal operation. Short-term uses of HFC-134a, on the other hand, are becoming an important source of emissions. Such uses include aerosols and open-cell foam blowing, which are denoted as short term because most of the HFC-134a used will be emitted to the atmosphere within a short period of time.
According to the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS), worldwide sales of HFC-134a for short-term applications jumped almost fourfold between 1994 and 1995. Sales for short-term uses leveled off at 10,500 metric tons in 1996 and then dropped to 6,500 metric tons in 1998; however, new developments in the U.S. market have reversed the downward trend, as sales of HFC-134a totaled 14,300 metric tons in 1999.92
In January 1999, the major marketers of tire inflaters began requiring the use of nonflammable material, creating additional demand for HFC-134a. Pennzoil was the first company to enter this new market, after removing its hydrocarbon-based canisters and reconfiguring them to use HFC-134a.93
For many years, the HFC-134a market was characterized by excess capacity and low prices, because the transition away from CFC-12 occurred more slowly than producers had expected.94 In 1998 and 1999, however, the market tightened considerably, as evidenced by a series of price increases. Driven in part by a demand surge triggered by an unusually hot summer in 1999, prices nearly doubled, rising from a low of $1.50 per pound to $2.50 per pound by September 1999. For the rest of 1999 and the first half of 2000, the market stabilized, with only one minor price increase in early 2000.
A number of HFC-134a producers are undertaking modest capacity expansion projects, including Dupont, INEOSFluor (formerly ICI Klea), and Honeywell (formerly AlliedSignal). More significant additions of new capacity are likely to be needed, however, given that capacity is increasing by only 2 to 3 percent per year, while global demand is growing by 10 percent. SRI International predicts that global demand will reach 20 million pounds by 2001; and according to a representative of Elf Atochem, the market will face significant supply shortages unless more investment in new capacity is undertaken over the next several years.95 The required capacity will presumably be built, but it is possible that the expansion in supply will lag behind the growth in demand. Anticipating and planning for this growth has proven to be a difficult challenge for producers, who must manage as best as possible an unprecedented transition from an established product (CFC-12) that is now under a global ban, to a new product (HFC-134a). In the long term, consumption and emissions of HFC-134a will continue to rise rapidly, although it is possible that capacity constraints may act as a brake on consumption in the near term.
1,1-Difluoroethane (HFC-152a)
As a non-ozone-depleting substance with a GWP of 120,96 HFC-152a is an attractive potential replacement for CFCs. It can be used as a blowing agent, an ingredient in refrigerant blends (e.g., in R-500), and in fluoropolymer manufacturing applications. There are no HFC-152a emissions associated with the latter application, because the HFC-152a is consumed in the manufacturing process. In 1996, 5 million pounds of HFC-152a was consumed in fluoropolymer manufacturing.97 HFC-152a is also compatible with the components used in aerosol products. Unlike CFCs, however, HFC-152a is flammable.
Only one U.S. company (DuPont) produces HFC-152a, using the trade name Dymel-152a. DuPont probably was producing HFC-152a at nearly full capacity in 1994, corresponding to production of about 8,000 metric tons. In 1995, the company reported having doubled its production capacity from 1992 levels to 15,875 metric tons.98 The company reported on its 1999 Form EIA-1605 that 1994 HFC-152a emissions peaked at 200 metric tons. By 1998, however, DuPont’s reported emissions had dropped to 40 metric tons. The EPA estimates HFC-152a emissions in 2000 at 1,552 metric tons of gas, an increase of 3.5 percent over the 1990 estimate.99
Other HFCs
Other hydrofluorocarbons with considerable radiative forcing potential include HFC-125 (C2HF5), HFC-143a (C2H3F3), HFC-227ea (C3HF7), HFC-236fa (C3H2F6), and HFC-4310 (C5H2F10), with 100-year GWPs of 3,400,4,300, 3,500, 9,400, and 1500 respectively.100 The EPA estimates total emissions of this group of “other HFCs” at 4.4 million metric tons carbon equivalent in 2000, representing 9.5 percent of all emissions of HFCs, PFCs, and SF6 reported (Table 30).101 Emissions of these HFCs are small but growing rapidly, as they continue to find applications as substitutes for CFCs. Emissions of “other HFCs” have increased by 10.5 percent since 1999.
HFC-125 is used in the blend R-410A, which is designed to replace HCFC-22 as the refrigerant of choice for stationary refrigeration and air conditioning applications.
Some manufacturers have already introduced air conditioners that use R-410A, but as yet the product has captured a small percentage of the market. As the phaseout of HCFC-22 begins to gain momentum, Honeywell expects a rapid increase in the demand for R-410A.102 The EPA estimates emissions of HFC-125 at 236 metric tons of gas in 1992, increasing to 1,561 metric tons in 2000 (Table 29). The estimate for 2000 is 21.1 percent higher than the estimate for 1999.103
HFC-143a is a halocarbon used in refrigeration and air conditioning, in blends such as R-404A, R-406A, R-408A, and R-507A. HFC-143a is used as a substitute because it contains neither chlorine or bromine and will not emit ozone-depleting halogen radicals into the stratosphere. Like other halocarbons, HFC-143a does make a positive contribution to atmospheric warming; however its GWP is lower than those of the gases it replaces, such as CFC-11 or those in the blend R-502. The EPA estimates 1993 emissions of for HFC-143a at 16 metric tons of gas, increasing to 903 metric tons in 2000. The 2000 estimate is 33.6 percent higher than the estimate for 1999.104
HFC-236fa is also used as a refrigerant, in particular by the U.S. Navy for shipboard applications.105 The EPA estimates 1997 emissions of HFC-236fa at 14 metric tons of gas, increasing to 297 metric tons in 2000. The estimate for 2000 is 39.4 percent higher than the estimate for 1999.106 Other HFCs and HFC blends are also likely to gain market share as a result of the phaseout, because no single product is suited for all applications. For example, each potential replacement product has an optimal operating temperature range; hence, the refrigerant best suited for use in ice cream freezers will differ from the best choice for milk coolers.107
In addition to replacing HCFC-22 in stationary air conditioning and refrigeration applications, other HFCs are expected to gain new markets as foam blowing agents. CFCs have already been phased out of this market, having been replaced by HCFCs (primarily HCFC-141b).
Among the potential replacements, HFC-245fa appears to be the strongest contender.108
Honeywell is building a world-scale plant in Louisiana for the production of HFC-245fa which will become fully operational by July 2002. Semi-commercial quantities of the product will be available from the plant in the third quarter of 2000.109 Honeywell is also developing blends that combine HFC-245fa with other materials to enhance its cost/performance ratio. To date, however, the foam blowing industry has failed to signal a clear preference for HFC-245fa or other alternatives. Instead, it continues to rely primarily on HCFC-141b while waiting to see which of the possible replacement candidates emerges as the preferred alternative.110 For some applications, non-fluorochemical alternatives (e.g., hydrocarbons) have been identified.111
Perfluorocarbons (PFCs)
PFCs are compounds composed of carbon and fluorine. PFC emissions are not regulated, although their high GWPs (5,700 for perfluoromethane [CF4] and 11,900 for perfluoroethane [C2F6]) 112 have drawn attention. PFCs are also characterized by long atmospheric lifetimes (up to 50,000 years); hence, unlike HFCs, they are essentially permanent additions to the atmosphere. The EPA estimates 2000 emissions of PFCs at 8.7 million metric tons carbon equivalent, slightly lower than 1999 emissions and 14.4 percent lower than 1990 emissions (Table 30).113
The principal quantifiable source of PFCs is as a byproduct of aluminum smelting created by the frequency and duration of anode effects during periods of process inefficiency. The EPA estimates U.S. emissions from aluminum production at 1,096 metric tons of perfluoromethane and 90 metric tons of perfluoroethane in 2000.114 Reductions in primary aluminum production and efficiency improvements to reduce anode effects have reduced emissions of perfluoromethane and perfluoroethane since 1990 by 55 percent and 64 percent, respectively. Many of the efficiency improvements have been achieved as a result of the EPA’s Voluntary Aluminum Partnership, which was launched in 1995. According to the U.S. Geological Survey, strong demand for aluminum in manufacturing passenger cars and light trucks is expected to increase overall consumption;115 however, domestic aluminum production declined in 2000 due to high energy costs and subsequent smelter production cutbacks.116
Another source of PFC emissions is semiconductor manufacturing. Perfluoromethane and perfluoroethane are used as etchants and cleaning agents in semiconductor manufacturing. The United States consumed an estimated 800 tons of perfluoroethane and perfluoromethane in 1995.117 For 2000, the EPA estimates emissions of perfluoromethane and perfluoroethane from semiconductor manufacturing at 286 metric tons and 431 metric tons of gas, respectively.118 Both estimates are 4.6 percent lower than the corresponding estimates for 1999 emissions. It is difficult to assess trends in PFC emissions from the semiconductor industry. On the one hand, the continued rapid expansion of the worldwide semiconductor market may lead to increased PFC use and emissions. On the other hand, industry efforts to curb emissions may help to offset these market forces to some extent.
A number of semiconductor manufacturing firms have joined an EPA program to reduce PFC emissions voluntarily.119 In 1999, the World Semiconductor Council, comprising manufacturers from Europe, the United States, Japan, and Korea, voluntarily committed to reduce emissions of PFCs by 10 percent from 1995 levels by 2010. In addition, a number of PFC distributors are developing PFC emissions control equipment.120 Abatement and other control options are commercially available and substitute chemicals that result in reduced emissions are being adopted.121
A variety of other perfluorinated compounds are used in the semiconductor industry, including C3F8 (which is manufactured by 3M and has a GWP of 8,600), C4F10 (GWP 8,600), C6F14 (GWP 9,000), NF3 (manufactured by Air Products), and CHF3.122
Sulfur Hexafluoride (SF6)
Sulfur hexafluoride (SF6) is used primarily as a dielectric in electrical transmission and distribution systems, specifically as an insulator for circuit breakers, switch gear, and other electrical equipment. In addition, its extremely low atmospheric concentration makes it useful as an atmospheric tracer gas for a variety of experimental purposes. Another important use of SF6 is as a cover gas during magnesium production and processing to prevent excessive oxidation of molten magnesium in the presence of air. Other sources of SF6 emissions include fugitive emissions from certain semiconductor manufacturing processes, and the occasional use of SF6 in experimental and specialized casting operations by the aluminum industry as a cover gas or a fluxing and degassing agent (using an industry-wide estimated 230,000 kilograms of SF6 per year in the United States and Canada).123 However, the latter estimate is highly uncertain and so slight that it is not included in models for SF6 emissions.
SF6 has a very high GWP of 22,200,124 but it is not emitted in large quantities. Recent improvements to EPA’s estimation methods have changed previous estimates of SF6 emissions (see discussion on "EPA Revises Emissions Estimation Methodologyt"). Based on new information, mainly from the Voluntary SF6 Emission Reduction Partnerships for Electric Power Systems and for the Magnesium Industry, the most recent EPA estimates show a steady decrease in U.S. SF6 emissions, from a peak of 1,672 metric tons of gas in 1993 to 909 metric tons in 2000, representing an overall decrease of 41.4 percent since 1990.125 While there is a growing demand for magnesium products from U.S. casting companies to meet the requirements of changing automobile designs, no substantial expansion in the U.S. magnesium production industry is expected. Foreign magnesium producers are expected to supply the growing U.S. demand.126
Ozone-Depleting Substances and Criteria Pollutants
In previous years, this chapter included emissions estimates and accompanying discussions for a variety of gases that have ambiguous effects on climate, including ozone-depleting substances—chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and bromofluorocarbons (halons). This chapter also covered the criteria pollutants—carbon monoxide (CO), nitrogen oxides (NOx), and nonmethane volatile organic compounds (NMVOCs)—which have indirect effects on climate through their effects on atmospheric concentrations of greenhouse gases. Currently, emissions estimates for those gases are not included in this chapter, because the ozone-depleting substances and criteria pollutants were excluded from the Kyoto Protocol. Furthermore, production of the ozone-depleting gases is being phased out under the Montreal Protocol. Although no longer included in the main body of this report, emissions estimates for ozone-depleting substances and criteria pollutants can be found in Appendix D, “Emissions Sources Excluded.”
URL: http://www.eia.doe.gov/oiaf/1605/ggrpt/other_gases.html