| Overview | Hydrofluorocarbons (HFCs) |
Perfluorocarbons (PFCs) |
| Sulfur Hexafluoride |
Chlorofluorocarbons (CFCs) |
Hydrochlorofluorocarbons (HCFCs) |
| Bromofluorocarbons (Halons) |
Other Chemicals |
Halocarbon Data Tables |
Emissions of the first group listed above continued their rapid rise in 1995. 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, HCFCs, and several other chlorine-containing gases have ambiguous effects on global climate change, because
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 gasesdescribed in this report. Emissions of ozone-depleting substances are, however, described in this
chapter, because their emissions are believed to have some effect on global climate.
Table 31 summarizes the 1995 U.S. emissions and global warming potentials of the halocarbons and other gases
described in this chapter. Establishments emitting more than 25,000 pounds annually of many ozone-depleting
substances are required to report their emissions, disposals, and recycling of the substances to the EPA's Toxics Release
Inventory (TRI).(60) These data exclude many greenhouse gases and most small-scale emissions, but they offer insight
into manufacturing emissions. Additionally, 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 it does not disaggregate emissions by country.(61)
Table 32 summarizes U.S. emissions by gas from 1989 to 1996. Emissions of CFCs have declined rapidly in the 1990s,
although the rate of decline appears to have slowed considerably in 1996. Emissions of HCFCs have expanded.
Emissions of HFCs, driven by rapid growth in the use of HFC-134a in motor vehicle air conditioners, have grown
rapidly in the past 3 years and will continue to do so through the 1990s. After declining in the early 1990s, emissions
of PFCs have begun to increase, due in part to the commercial introduction of new PFCs. New perfluoropolyethers
(PFPEs) have also been introduced onto the market. Emissions of other gases (such as methyl chloroform), which are
either ozone-depleting substances or carcinogens, or both, have declined considerably in recent years.
Table 33 shows U.S. emissions (in million metric tons carbon equivalent) of those gases for which reliable global
warming potentials (GWPs) have been developed. GWPs represent estimates of the relative impacts on global warming
of various greenhouse gases, compared with that of carbon dioxide. As such, they can be used to convert emissions
estimates for different gases
into equivalent carbon emissions for comparative purposes. CFCs, HFCs, HCFCs, and PFCs generally are highly potent
greenhouse gases, with large GWPs. Hence, the carbon-equivalent emissions of these gases (Table 33) are often several
orders of magnitude larger than their actual emissions (Table 32).
HFCs are compounds containing carbon, hydrogen, and fluorine. 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. On its Form EIA-1605, DuPont reported emissions of about 1,100 metric tons ofHFC-23 in 1995.(62)
Total U.S. emissions are estimated at between 2 and 4 percent of total HCFC-22 production, implying 3,000 to 5,000
metric tons per year.(63) 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 HFC-23 emissions.
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 are growing 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.(64) 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. HFC-134a conversion packages are now
available for older cars.
Automobile air conditioners are subject to leakage, with sufficient refrigerant leaking out (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 emissions
of nearly 1,000 metric tons from GM-made vehicles on the road in 1995. GM based this estimate on an assumed annual
leakage rate of 10 percent per year. Given that GM controls roughly one-third of the U.S. automobile market, the
reported GM emissions value implies that total U.S. HFC-134a emissions from mobile air conditioners were equal to
about 3,000 metric tons in 1995. Emissions from this source are expected to increase dramatically in the near future,
as the replacement of vehicles using CFCs proceeds at a rapid pace.
HFC-134a is also used as a refrigerant in most new refrigerators built in the United States and in commercial chillers,
but leakage from these sources is much less significant than that 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 a significant source of emissions.
According to AFEAS, worldwide sales of HFC-134a for short-term applications (including aerosols and open-cell foam
blowing) jumped almost fourfold between 1994 and 1995, reaching 10,500 metric tons, or 14 percent of total 1995 sales
for all uses.(65) HFC-134a has the distinct advantage of being the only nonflammable liquefied gas propellant available
on the market. The EPA estimated total 1995 emissions of HFC-134a at about 11,000 metric tons.
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.(66) DuPont scientists believe that HFC-152a will
capture the primary share of the propellant market, because it is less expensive than HFC-134a (the primary
alternative), has a much lower GWP, and is a better solvent (an important characteristic if ingredients are to remain
in solution).(67) DuPont probably was producing HFC-152a at nearly full capacity in 1994, corresponding to production
of about 8,000 metric tons. The company reported 1994 HFC-152a emissions of 180 metric tons on its Form EIA-1605.
In 1995, however, DuPont's reported emissions dropped to only 18 metric tons. The EPA estimated 1990 emissions of
HFC-152a at only 300 metric tons, rising to 1,500 metric tons in 1994, then dropping back to 900 metric tons in 1995.
Several other "new" hydrofluorocarbons with considerable radiative forcing potential are beginning to appear on the
market. They include HFC-32 (CH2F2) and HFC-125 (C2HF5), with 100-year GWPs of 650 and 2,800, respectively, both
of which are used as com-ponents in refrigerant blends. The EPA estimated 1995 emissions of HFC-125 at 2,270
metric tons.(68) Other prospective HFCs include HFC-143a (C2H3F3), HFC-227ea (C3HF7), and HFC-236fa (C3H2F6), with
100-year GWPs of 3,800, 2,900, and 6,300, respectively. The EPA has estimated 1995 emissions of HFC-227ea at 1,860
metric tons and HFC-143a emissions at 40 metric tons.
Perfluorocarbons are compounds composed of carbon and fluorine. Because 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. 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 (CCAP). PFCs are also
characterized by long atmospheric lifetimes (up to 50,000 years); hence, unlike HFCs, they are essentially permanent
additions to the atmosphere. As byproducts of aluminum production, they arise during discrete periods of process
inefficiency. Emissions can be reduced by improving process efficiency. The Voluntary Aluminum Industrial
Partnership, aimed at reducing PFC emissions from the aluminum industry, is a CCAP initiative.
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.(69) These coefficients, in conjunction with aluminum production
figures, suggest U.S. emissions of 2,030 metric tons of perfluoromethane and 203 metric tons of perfluoroethane in 1995.
Another source of PFC emissions is semiconductor manufacturing. Perfluoromethane and perfluoroethane are used
as etchants and cleaning agents in semiconductor manufacturing. Although anywhere from 5 to 95 percent of the CF4
and C2F6 is destroyed, the process produces fugitive emissions of perfluoroethane, perfluoromethane, and sulfur
hexafluoride. The U.S. consumed an estimated 800 tons of perfluoroethane and perfluoromethane in 1995.(70) PFC
emissions from the semiconductor industry are believed to account for 5 to 10 percent of total U.S. emissions.(71) 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 60 to 70
percent of GWP-weighted emissions caused by perfluoroethane.(72) 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 quantify trends in emissions of these chemicals used by the semiconductor industry;
however, qualitative information suggests that emissions may grow more slowly in the future. Since 1992, DuPont--the
sole manufacturer of perfluoroethane--has been asking its customers to limit PFC use.(73) More recently, 23
semiconductor manufacturing firms joined a new EPA program to reduce PFC emissions voluntarily. In addition, a
number of PFC distributors are developing PFC emissions control equipment.(74)
A variety of other perfluorinated compounds are beginning to be used in the semiconductor industry, including C3F8
(manufactured by 3M), C4F10 (with aGWP of 7,000), C6F14 (with a GWP of 7,400), NF3 (manufactured by Air Products),
and CHF3. The EPA estimates 1995 emissions of PFCs and PFPEs (exclusive of perfluoromethane and perfluoroethane)
at 1,030 metric tons.(75)
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 atmospheric tracer gas for a variety of
experimental purposes. 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.(76) 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. EPA's estimates indicate an increase in emissions between 1994 and 1995,
from 1,030 metric tons to 1,290 metric tons.(77)
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,(78) accounting for
a small fraction of estimated emissions.
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. Although molecule for molecule they absorb thousands of times more
infrared radiation than does 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.(79)
The Copenhagen Amendments of the Montreal Protocol suggested 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 specify 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. Emissions of CFCs contained in mobile air conditioners, chillers, and other equipment built prior to the
regulations will continue at least into the next decade. As just one example, the EPA estimates that in 1999 80,000 CFC-using centrifugalchillers--57 percent of the total--will still be in service.(80)
CFC-11 is used principally as a blowing agent for foams and packaging materials and as a refrigerant in large
commercial chillers. Sales have been declining steadily since 1989, with production following roughly the same trend,
except for a spike in 1992.(81) In 1994, production and sales declined by
nearly 80 percent, to only 7,000 metric tons,(82)
implying that CFC-11 has been phased out of the blowing agent market completely, with residual CFC-11 probably
used only to recharge existing 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. Furthermore, existing CFC-11 chillers are
being replaced by new chillers, as evidenced by the sharp 32-percent increase in U.S. chiller sales between 1994 and
1995.(83) According to a DuPont spokesperson, chiller retrofits are being performed at the rate of 1,000 units per year,
and chiller replacements are being made at the rate of 4,000 units per year.(84) Nonetheless, chiller replacements are
proceeding more slowly than originally expected, according to a survey released by the Air Conditioning and
Refrigeration Institute (ARI).(85)
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. Pursuant to the Montreal Protocol, production and sales dropped dramatically in
1990 and 1991, falling below estimates of end-use applications and emissions. In recent years, end use has gradually
declined as CFCs are phased out (Figure 10).(86)
AFEAS data suggest that use of CFC-12 as a blowing agent dropped by more than 90 percent between 1988 and 1995.(87)
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.
With production of CFC-12 ending and prices rising sharply, a significant black market in CFCs has developed. A
number of individuals have been arrested for smuggling CFC-12 into the United States, particularly in Florida.(88)
Houston has also become a major port of entry for CFCs smuggled in from Mexico. As of mid-1996, U.S. Customs
believed that CFC-12 was the most commonly smuggled commodity after illicit drugs.(89)
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. In the next few years,however, 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.
Approximately 40 million pounds of CFC-12--about two-thirds of total U.S. consumption--are used each year to
recharge mobile air conditioners. However, the high prices and limited availability of CFC-12 will increasingly force
people to discard or retrofit rather than repair CFC-using equipment when it fails.
CFC-113, also known as "freon 113," is used principally 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 1989. In 1995, emissions of CFC-113 reported in the
Toxics Release Inventory (TRI) were about 1,180 metric tons--down substantially from 11,000 metric tons in 1992.(90)
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 used principally 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.(91) 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 460 metric tons in 1995.(92)
CFC-115 is used primarily as a blending agent for some specialty refrigerants. Northern hemisphere sales in
1994 were only 7,000 metric tons.(93) Emissions as reported in the TRI were less than 300 metric tons per year in the early
1990s, declining to 130 metric tons in 1995.(94)
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, which 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, although 1995 saw a more substantial increase of 10 percent.
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 forclosed-cell
foams, with a net GWP of 270. Northern hemisphere sales rose from less than 1,000 metric tons in 1990 to 112,000
metric tons in 1995.(95) Emissions as reported in the 1995 TRI totaled 5,000 metric tons.(96) 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 1996.
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. Worldwide production doubled between 1990 and
1994, from 19,000 metric tons to 38,000 metric tons, but production appears to be stabilizing, having increased by only
1 percent between 1994 and 1995. Most HCFC-142b (more than 80 percent in 1995) is sold for long-lifetime
applications--particularly as a blowing agent for closed-cell foams.(97) Total emissions as reported in the 1995 TRI were
3,150 metric tons.(98)
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 50 and 340 metric tons, respectively, in 1995.(99) The EPA
estimates 1994 total HCFC-124 emissions at 2,000 metric tons. The EPA believes that 1990 emissions of these chemicals
were negligible.
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;
consequently, production will cease in 1996 under 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.
Several other chemicals combine high GWPs and significant emissions levels to produce potential effects 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.(100)
Production and sales data for carbon tetrachloride have not been available in recent years. The TRI listed 1995
emissions of carbon tetrachloride at roughly 200 metric tons, down from nearly 300 metric tons in 1994.(101) The TRI
suggests that about 900 metric tons were recycled in 1995 and an additional 24,400 metric tons destroyed. Emissions
estimates presented in Table 32 were developed from sales data and production data for CFC-11 and CFC-12. A rough
approximation of emissions is determined by calculating (on a stoichiometric basis) theportion 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. Used primarily as a solvent, it was required to be phased out by 1996. It
has indirect cooling effects akin to those of carbon tetrachloride and the CFCs, but its GWP is only 110. As a result, its
net effect is likely to promote global cooling.(102) Estimated emissions have been declining rapidly, from 316,000 metric
tons in 1990 to only 46,000 metric tons in 1995 (Table 32). In 1995, the TRI reported emissions (presumably largely from
manufacturers) of 10,300 metric tons, with recycling of 28,900 metric tons and disposals of 3,200 metric tons.(103)
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 a carcinogen, chloroform is reported to the TRI. The TRI indicates that emissions
have been decreasing and were only 4,800 metric tons in 1995.(104)
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 small. A potential carcinogen, methylene chloride emissions are regulated and
included in the TRI, with 1995 emissions of 26,000 metric tons, down significantly from 46,000 metric tons in 1990. The
TRI indicates substantial activity in recycling and disposal, with about 45,000 metric tons recycled and 21,000 metric
tons undergoing disposal in 1995.(105)
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