| Overview | Chlorofluorocarbons (CFCs) |
| Hydrochlorofluorocarbons (HCFCs) |
Hydrofluorocarbons (HFCs) |
| Bromofluorocarbons (Halons) |
Perfluorocarbons (PFCs) |
| Other Chemicals |
Halocarbon Data Tables |
| Total U.S. Emissions of Hydrofluorocarbons,
Perfluorocarbons, and Sulfur Hexafluoride, 1990-1994 | |
| Estimated 1994 Emissions (Million Metric Tons Carbon Equivalent) | 29.5 |
| Change Compared to 1993 (Million Metric Tons Carbon Equivalent) | 3.5 |
| Change from 1993 (Percent) | 13.4 |
| Change Compared to 1990 (Million Metric Tons Carbon Equivalent) | 4.5 |
| Change from 1990 (Percent) | 18.1 |
Emissions of halocarbons and other gases with unambiguous global warming effects (hydrofluorocarbons [HFCs], perfluorocarbons [PFCs], and sulfur hexafluoride) have risen rapidly, though from very low levels, in recent years. HFCs were first widely used commercially in the 1990s, when they were introduced as replacements for chlorofluorocarbons (CFCs), whose use is being phased out, pursuant to the Montreal Protocol, because they damage the Earth’s ozone layer.
CFCs, hydrochlorofluorocarbons (HCFCs), and several other chlorine-containing gases, have ambiguous effects on global climate change, since their capacity to absorb reflected infrared radiation is offset to some degree by their tendency to react with ozone, which is itself a greenhouse gas. Hence, ozone-depleting substances are not directly included in the total emissions of greenhouse gases described in this report. Emissions of ozone-depleting substances are, however, described in this chapter, since their emissions are believed to have some effect on global climate.
Table 31 summarizes the 1994 U.S. sales, emissions, and global warming potentials of the halocarbons and other gases described in this chapter. U.S. production and sales of many of these chemicals are surveyed by the International Trade Commission [54]. Establishments emitting more than 25,000 pounds annually of many ozone-depleting substances are required to report their emissions, disposals, and recycling of these substances to the EPA’s Toxics Release Inventory (TRI) [55]. These data exclude many greenhouse gases and most small-scale emissions, but they offer insight into manufacturing emissions. Finally, the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS) reports on production, sales, and emissions of a range of manufactured greenhouse gases and ozone-depleting substances for most of the world, but does not disaggregate emissions by country [56].
Table 32 summarizes emissions by gas from 1988 to 1995. Emissions of CFCs have declined rapidly in the 1990s, while emissions of HCFCs have expanded. Emissions of HFCs, sparked by the rapid growth in use of HFC-134a in motor vehicles, have grown rapidly in the past 2 years and will continue to do so through the 1990s. Estimated emissions of PFCs have declined in recent years along with declining aluminum production in the United States. Emissions of other gases, which are either ozone-depleting substances, carcinogens, or both, have declined considerably in recent years.
CFCs are derivatives of hydrocarbons, which are composed of carbon and hydrogen atoms. In CFCs, the hydrogen atoms are replaced with chlorine and fluorine atoms, yielding an array of nontoxic, nonflammable gases useful in a wide variety of applications. CFCs have no natural source, and their high molecular stability allows them to migrate to the stratosphere, where they destroy ozone. Though molecule for molecule they absorb thousands of times more infrared radiation than carbon dioxide, their net warming affect is reduced because of their effect on ozone. Ozone (O3), beneficial in the stratosphere for its ability to absorb harmful ultraviolet radiation, is also a potent greenhouse gas. Thus, while the direct effect of CFCs is a warming potential far greater than that of carbon dioxide, their indirect effect on ozone reduces their net radiative forcing effects by half [57].
The Copenhagen Amendments of the Montreal Protocol suggest phasing out CFCs by 1996. The United States is implementing these provisions through the Clean Air Act Amendments of 1990 and subsequent EPA regulations, which include allowable production quotas and taxes on inventories and stocks. All production ceased in January 1996, with the exception of small amounts used in metered dose inhalers for asthma patients, for which no substitutes are available.
CFC-11 is principally used as a blowing agent for foams and packaging materials and as a refrigerant in large commercial chillers. Sales have been declining steadily since 1988, with production following roughly the same trend, except for a spike in 1992 [58]. In 1994, production and sales declined by nearly 80 percent, to only 7,000 metric tons [59]. This implies that CFC-11 has been phased out of the blowing agent market completely, and residual CFC-11 is probably used only for chillers. This will be a shrinking source of emissions, as no new CFC-11 chillers are being built, and existing chillers are likely to be retrofitted to use other coolants.
CFC-12 is often known by its trade name, “freon-12.” Exceedingly versatile, its end uses include air conditioning (both automotive and commercial); refrigeration (refrigerators and freezers of varying scales); and as a blowing agent for foams, insulations, and packaging. The signing of the Montreal Protocol in 1987 caused trends in its production, sales, and emissions to fluctuate. Before 1987, the production, sale, and end use of CFC-12 were all nearly equivalent. In 1988 and 1989, production and sales were well above the estimated amount of CFC-12 being incorporated in end uses, suggesting that end users were stockpiling the compound in response to the expected cessation of U.S. production. Production and sales dropped dramatically in 1990 and 1991, falling below estimates of end-use applications and emissions. In recent years, the four figures have once again become consistent, with end use gradually declining as CFCs are phased out (Figure 11) [60].
AFEAS data suggest that use of CFC-12 as a blowing agent decreased by nearly 90 percent between 1988 and 1994 [61]. The use of CFC-12 in refrigeration, however, declined more slowly until 1994. During 1994, automobile, refrigerator, and commercial chiller manufacturers essentially ceased using CFC-12 in their products completely.
In the past year, with production of CFC-12 ending and prices rising sharply, their has been an epidemic of CFC smuggling, particularly from Eastern Europe. A number of individuals have been arrested for smuggling CFC-12 into the United States, particularly in Florida [62]. U.S. Customs believes that CFC-12 may now be the most commonly smuggled commodity after illicit drugs.
Current emissions of CFC-12 from the now dwindling stock of existing equipment are probably on the order of 60,000 to 70,000 metric tons. However, in the next few years, emissions should decline rapidly. At present, emissions are being sustained by the large stock of CFC-using equipment, such as refrigerators and automobile air conditioners. However, the high prices and limited availability of CFC-12 will increasingly encourage people to discard or retrofit rather than repair CFC-using equipment when it fails.
CFC-113, also known as “freon 113,” is principally used as a solvent. In particular, it is a useful cleaner for electronic circuit boards, because it volatilizes easily and will not damage the circuitry. Such an end use, and others consistent with it as detailed in AFEAS, imply that emissions of CFC-113 are roughly equivalent to production.
Estimated emissions of CFC-113 have been declining rapidly since 1988. In 1994, emissions of CFC-113 reported in the TRI were about 2,300 metric tons—down substantially from the 11,000 metric tons in 1992 [63]. Recycling and treatment of CFC-113 have also declined in recent years, indicating that CFC-113 is being phased out in favor of alternatives.
CFC-114 is principally used as a solvent. According to AFEAS, roughly two-thirds of all CFC-114 sales go toward short-lifetime end uses, such as cleaning and drying agents, with the rest being used in closed-cell foams and refrigeration applications, where the compound may remain trapped for up to 12 years [64]. In addition, the U.S. Department of Energy uses CFC-114 in the enrichment of uranium. Emissions reported in the TRI, which are a reasonable proxy for industrial emissions, were only 600 metric tons [65].
CFC-115 is used primarily as a blending agent for some specialty refrigerants. Northern hemisphere sales in 1994 were only 7,000 metric tons [66]. U.S. emissions in the early 1990s were less than 300 metric tons annually, declining to 150 metric tons in 1994 [67].
Hydrochlorofluorocarbons (HCFCs)
HCFCs are essentially CFCs that include one or more hydrogen atoms. The presence of hydrogen makes the resulting compounds less stable, and as a result they are more susceptible to photodecomposition, have much shorter atmospheric lifetimes than CFCs, and consequently are less likely to migrate to the stratosphere where they would destroy ozone. As a result, they are popular interim substitutes for CFCs. The Copenhagen Amendments placed HCFCs under control, with HCFC-22 slated for elimination by 2020 and all others by 2030. HCFCs still have high GWPs, and these are compounded by the fact that they have weaker indirect cooling effects than do CFCs.
HCFC-22 is the most commonly used refrigerant for home air conditioning systems. It is the most widely available and least expensive potential substitute for CFCs in a variety of applications. However, the available evidence suggests that HCFC-22 gained most of its market share at the expense of CFCs in the late 1980s. Total U.S. sales of HCFC-22 declined from 108,000 metric tons in 1991 to 97,000 metric tons in 1994. Production has historically exceeded sales by a substantial margin.
Estimated emissions of HCFC-22 have been rising slowly. AFEAS data suggest that the increased usage of HCFC-22 for long- and medium-lifetime uses has created a “banked” inventory of the compound that is now being emitted.
HCFC-141b is a relatively new commercial product, used primarily as a solvent and as a blowing agent for closed-cell foams, with a net GWP of 270. Northern hemisphere sales rose from less than 1,000 metric tons in 1990 to 78,000 metric tons in 1994 [68]. The EPA estimates 1994 U.S. emissions of HCFC-141b at 16,000 metric tons [69]. Based on the extensive use of HCFC-141b in solvents and closed-cell foams, it is likely that emissions of this chemical expanded substantially in 1995.
HCFC-142b is a CFC replacement with a net GWP of 1,650. U.S. production and sales data are not available. AFEAS collects information on worldwide production, which taken in conjunction with information on northern hemisphere sales can be used to estimate a ceiling on U.S. sales or emissions. In 1994, worldwide production continued to grow, reaching nearly 40,000 metric tons [70]. Of that amount, approximately 3,000 metric tons were sold for short-lifetime end uses, including sterilants, inhalers, and open-cell foams [71]. The EPA estimated 1994 emissions of HCFC-142b at 10,000 metric tons [72]. This figure implies that most of the worldwide production of HCFC-142b may be taking place in the United States. Based on the growing use of HCFC-142b for closed-cell foam applications, it is likely that emissions increased substantially in 1995.
A number of HCFCs may gain importance as CFCs are phased out in the near future. HCFC-123 is a potential replacement for CFC-11 in refrigeration applications, and HCFC-124 is a potential replacement for CFC-12 in sterilizers. The TRI reported HCFC-123 and HCFC-124 emissions of 2,400 and 380 metric tons, respectively, in 1994 [73]. The EPA estimates 1994 total HCFC-124 emissions at 2,000 metric tons. The EPA believes that 1990 emissions of these chemicals were negligible.
| U.S. Emissions of Hydrofluorocarbons,
1990-1994 | |
| Estimated 1994 Emissions (Million Metric Tons Carbon Equivalent) | 18.6 |
| Change Compared to 1993 (Million Metric Tons Carbon Equivalent) | 3.8 |
| Change from 1993 (Percent) | 25.7 |
| Change Compared to 1990 (Million Metric Tons Carbon Equivalent) | 5.3 |
| Change from 1990 (Percent) | 39.8 |
HFCs are hydrochlorofluorocarbons without the chlorine. Because they contain only carbon, hydrogen, and fluorine, they do not destroy ozone. Consequently, they are a desirable CFC replacement. Ironically, the characteristic that makes them a desirable replacement from an ozone perspective also makes them potent greenhouse gases with no offsetting indirect effects.
The market for HFCs is expanding as CFCs are being phased out. It is difficult to keep pace with the variety of HFCs that are being developed and the quantities being produced. Consequently, accurate data are difficult to obtain.
HFC-23 is created as a byproduct in the production of HCFC-22. Small amounts are also used in semiconductor manufacture. Emissions are estimated at between 2 and 4 percent of total HCFC-22 production, implying a total of 3,000 to 5,000 metric tons per year [74]. Although this total seems small, the GWP of HFC-23 is very large at 11,700—giving it a substantial direct effect without any known offsetting indirect effects. The Climate Change Action Plan includes a voluntary program with HCFC-22 producers to reduce emissions and explore potential markets for HFC-23 as a halon replacement and refrigerant.
HFC-134a, with a GWP of 1,300, is gaining importance as a replacement for CFCs, especially in automotive air conditioners. Emissions for 1990 were estimated at only 500 metric tons, but they will likely grow significantly as HFC-134a gains market share. In 1993, Ford sold nearly 40,000 vehicles each of which used approximately 2 pounds of HFC-134a in its air conditioner [75]. Previous models used about 2.5 pounds of CFC-12. Essentially all 1994 and subsequent model year automobiles use HFC-134a as the refrigerant in their air conditioners. Many manufacturers now offer HFC-134a conversion packages for older cars through their dealerships.
Automobile air conditioners are subject to significant leakage, with sufficient refrigerant leaking out (30 percent or more of the charge) over a 5-year period to require servicing. This would suggest that 1993 emissions of HFC-134a from automotive sources totaled only 15 metric tons. In 1994, however, with millions of new vehicles using HFC-134a, automotive emissions may have risen by two orders of magnitude. With increased production and usage of HFC-134a in replacement applications, emissions are expected to increase dramatically in future years.
HFC-134a is also used as refrigerant in most new refrigerators built in the United States, in commercial chillers, and to a limited extent as a solvent and blowing agent.
The EPA estimated 1994 emissions of HFC-134a at about 10,000 metric tons, and 1995 emissions should be at least 50 percent higher than 1994 emissions.
As a non-ozone-depleting substance with a GWP of only 140, 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. It is also compatible with the components used in aerosol products. Unlike CFCs, however, HFC-152a is flammable.
Only one company (DuPont) produces HFC-152a, using the trade name Dymel-152a, and in 1995 the company reported having doubled its production capacity to 35 million pounds since 1992 [76]. Consequently, DuPont probably was producing HFC-152a near full capacity in 1994. This corresponds to production of about 8,000 metric tons, which places a ceiling on emissions. The EPA estimated 1990 emissions of HFC-152a at only 300 metric tons, rising to 1,500 metric tons by 1994. The doubling of production capacity implies that 1995 emissions were considerably higher than 1994 emissions. As HFC-152a gains market share forfeited by CFCs and replacements with higher GWPs, emissions are likely to increase significantly in future years.
Several other “new” hydrofluorocarbons with considerable radiative forcing potential are beginning to appear on the market. These include HFC-32 (CH2F2) and HFC-125 (C2HF5), with 100-year global warming potentials of 650 and 2,800, respectively, both of which are used as components in refrigerant blends. The EPA estimated 1994 emissions of HFC-125 at about 1,000 metric tons [77]. Other prospective HFCs include HFC-143a (C2H3F3), HFC-227ea (C3HF7), and HFC-236fa (C3H2F6), with 100-year global warming potentials of 3,800, 2,900, and 6,300, respectively. The EPA has estimated 1994 emissions of HFC-227ea at about 900 metric tons.
Bromofluorocarbons are similar to CFCs except that they contain at least one bromine atom. They are inert, nontoxic, and evaporate without leaving any residue, making them popular for use as fire suppressants for high-value equipment such as computer centers and aircraft. The trade name “halon” is applied to several of these chemicals, which are used as fire suppressants. Halons are particularly destructive to stratospheric ozone, and consequently production will cease in 1996 as per agreements in the Montreal Protocol. The U.S. military, which uses a significant volume of halons to protect sensitive equipment, is involved in a program to reduce emissions through recycling, using substitutes, and preventing leakage of halons in existing systems. Emissions of halons are low, although the exact figure is uncertain. The EPA estimated 1994 emissions at 2,000 metric tons for halon-1301 and 1,000 metric tons for halon-1211.
| U.S. Emissions of Perfluorocarbons,
1990-1994 | |
| Estimated 1994 Emissions (Million Metric Tons Carbon Equivalent) | 4.2 |
| Change Compared to 1993 (Million Metric Tons Carbon Equivalent) | -0.5 |
| Change from 1993 (Percent) | -10.7 |
| Change Compared to 1990 (Million Metric Tons Carbon Equivalent) | -1.0 |
| Change from 1990 (Percent) | -18.5 |
Perfluorocarbons are hydrocarbons in which the hydrogen has been replaced by fluorine. Since they contain no chlorine, they are not harmful to ozone and therefore do not possess the indirect cooling effects of CFCs. As a result, they are unambiguously greenhouse gases. The principal quantifiable source of PFCs is as a byproduct of aluminum smelting. The EPA estimates that 0.6 kilogram of perfluoromethane (CF4, also known as carbon tetrafluoride) and 0.06 kilogram of perfluoroethane (C2F6) are emitted as a result of each metric ton of aluminum smelted [78]. These coefficients, in conjunction with aluminum production figures, suggest U.S. emissions of 2,200 metric tons of perfluoromethane and 220 metric tons of perfluoroethane in 1993. Perfluoromethane is also emitted during the process of uranium enrichment, at a rate that probably is less than 20 metric tons per year [79]. Another minor emissions source is a National Aeronautics and Space Administration hypersonic wind tunnel.
The principal source of PFC emissions, after aluminum smelting, is probably semiconductor manufacturing. Perfluoroethane is used as a purging agent in semiconductor manufacturing. The process produces fugitive emissions of perfluoroethane, perfluoromethane, and sulfur hexafluoride. The sole U.S. producer, DuPont, reports that it plans to double its perfluoroethane production capacity in 1995, while encouraging customers to reduce their emissions by 80 percent [80]. The EIA has not yet been able to ascertain DuPont’s current actual capacity or production of the chemical. However, available information suggests that sales of perfluorethane were probably less than 1,000 metric tons in 1994 [81]. Perfluoromethane (CF4) is also produced commercially in small quantities. The EPA’s Atmospheric Pollution Prevention Division believes that emissions of PFCs, HFC-23, and sulfur hexafluoride from the semiconductor industry totaled about 1 million metric tons carbon equivalent in 1994, with about 70 percent of GWP-weighted emissions caused by perfluoroethane [82]. This is equivalent to emissions of about 300 metric tons of perfluoroethane and considerably smaller amounts of the other gases. The EIA is unable at present to assess trends in emissions of these chemicals used by the semiconductor industry.
PFC emissions are not regulated or reported, although their high GWPs (6,900 for perfluoromethane and 9,200 for perfluoroethane) have drawn the attention of the Climate Change Action Plan. As a byproduct of aluminum production, they arise during discrete periods of process inefficiency. Emissions could be reduced by improving process efficiency.
Several other chemicals combine both high GWPs and emissions levels to have a potential effect on global climate: carbon tetrachloride, methyl chloroform, chloroform, methylene chloride, and sulfur hexafluoride. Several of these chemicals are regulated under the Clean Air Act Amendments of 1990.
Carbon tetrachloride is a chemical whose uses have varied. Originally used as a household cleanser and dry-cleaning solvent, it was determined to be carcinogenic, and such uses were terminated. Most carbon tetrachloride is now used as a feedstock in the production of CFC-11 and CFC-12. Carbon tetrachloride is regulated by the Clean Air Act Amendments as a known carcinogen, and under the Montreal Protocol as an ozone-depleting chemical. Its production was phased out in January 1996. Much like CFCs, carbon tetrachloride has a high direct GWP (1,400), which is completely offset by its indirect cooling effect of destroying ozone. Its net effect favors global cooling [83].
Production and sales data have not been available in recent years [84]. The TRI listed 1993 emissions of carbon tetrachloride at roughly 1,000 metric tons, up from 650 metric tons in 1992 [85]. The TRI suggests that about 50 metric tons were recycled in 1993, down from nearly 160 metric tons in 1993. Estimates presented in Table 32 were developed using sales data and production data for CFC-11 and CFC-12. A rough approximation of emissions is determined by calculating (on a stoichiometric basis) the portion of total carbon tetrachloride sales that goes toward production of CFCs, and assuming that the rest is used as a solvent and consequently emitted to the atmosphere.
Like carbon tetrachloride, methyl chloroform is regulated under the Clean Air Act Amendments as an ozone-depleting chemical covered by the Montreal Protocol. Primarily used as a solvent, it is required to be phased out by 1996. It has indirect cooling effects akin to carbon tetrachloride and the CFCs, but its GWP is only 110. As a result, its net effect is likely to promote global cooling [86]. U.S. sales of methyl chloroform continued to decline in 1994, down to 166,000 metric tons [87]. However, emissions as estimated by EPA declined even more rapidly, to 78,000 metric tons in 1994. This figure leaves about 88,000 metric tons of methyl chloroform unaccounted for. In 1994, the TRI reported emissions (presumably largely from manufacturers) of 17,000 metric tons, with recycling of 3,000 metric tons and disposals of 2,000 metric tons [88]. Estimates of emissions are shown in Table 32.
Chloroform is used primarily as a feedstock for HCFC-22, with secondary use as a solvent. It is a fairly weak greenhouse gas with a GWP of 5. Total emissions should be low, because most chloroform is incorporated into HCFC-22 during its production. As chloroform is a carcinogen, it is reported to the TRI. The TRI indicates that emissions have been decreasing and were only 5,200 metric tons in 1994 [89].
Like chloroform, methylene chloride is a weak greenhouse gas (GWP of 9). Its short atmospheric lifetime of less than 1 year probably prevents it from reaching the stratosphere where it would be damaging to ozone. As a result, its indirect cooling effects are likely to be quite small. A potential carcinogen, methylene chloride emissions are regulated and included in the TRI, with 1994 emissions of 29,000 metric tons, down significantly from 46,000 metric tons in 1990 [90]. The TRI indicates substantial activity in recycling and disposal, with about 9,000 metric tons recycled and 7,000 metric tons undergoing disposal in 1994.
| U.S. Emissions of Sulfur Hexafluoride,
1990-1994 | |
| Estimated 1994 Emissions (Million Metric Tons Carbon Equivalent) | 6.7 |
| Change Compared to 1993 (Million Metric Tons Carbon Equivalent) | 0.2 |
| Change from 1993 (Percent) | 3.0 |
| Change Compared to 1990 (Million Metric Tons Carbon Equivalent) | 0.2 |
| Change from 1990 (Percent) | 3.0 |
Sulfur hexafluoride (SF6) is used as an insulator for circuit breakers, switch gear, and other electrical equipment. In addition, its extremely low atmospheric concentration makes it a useful test gas for the calibration of gas concentration monitors. It is also a fugitive emission from certain semiconductor manufacturing processes.
Sulfur hexafluoride has a high GWP of 23,900, but it is not produced or used in large quantities. In 1989, global production and emissions were estimated at 5,000 metric tons [91]. The EPA estimates annual U.S. production of sulfur hexafluoride at 6,000 metric tons and emissions at about 1,000 metric tons annually. This is equivalent to emissions of more than 6 million metric tons of carbon.
The EPA’s Atmospheric Pollution Prevention Division reports that sulfur hexafluoride is also used in small amounts in the semiconductor industry and also as a cover gas in magnesium manufacturing and die casting [92]. The EPA estimates magnesium-related sulfur hexafluoride emissions at 1.2 million metric tons carbon equivalent, or about 200 metric tons of sulfur hexafluoride. The EIA is unable at present to assess trends in sulfur hexafluoride emissions from magnesium manufacture.
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