Chlorofluorocarbons (CFCs) are fully halogenated paraffin hydrocarbons that contain only carbon (С), chlorine (Cl), and fluorine (F), produced as volatile derivative of methane, ethane, and propane. They are also commonly known by the DuPont brand name Freon. The most common representative is dichlorodifluoromethane (R-12 or Freon-12). Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), and solvents. Because CFCs contribute to ozone depletion in the upper atmosphere, the manufacture of such compounds has been phased out under the Montreal Protocol, and they are being replaced with other products such as hydrofluorocarbons (HFCs)[1] (e.g., R-410A) and R-134a.[2][3]

Structure, properties and production

As in simpler alkanes, carbon in the CFCs bonds with tetrahedral symmetry. Because the fluorine and chlorine atoms differ greatly in size and effective charge from hydrogen and from each other, the methane-derived CFCs deviate from perfect tetrahedral symmetry.[4]

The physical properties of CFCs and HCFCs are tunable by changes in the number and identity of the halogen atoms. In general, they are volatile but less so than their parent alkanes. The decreased volatility is attributed to the molecular polarity induced by the halides, which induces intermolecular interactions. Thus, methane boils at −161 °C whereas the fluoromethanes boil between −51.7 (CF2H2) and −128 °C (CF4). The CFCs have still higher boiling points because the chloride is even more polarizable than fluoride. Because of their polarity, the CFCs are useful solvents, and their boiling points make them suitable as refrigerants. The CFCs are far less flammable than methane, in part because they contain fewer C-H bonds and in part because, in the case of the chlorides and bromides, the released halides quench the free radicals that sustain flames.

The densities of CFCs are higher than their corresponding alkanes. In general, the density of these compounds correlates with the number of chlorides.

CFCs and HCFCs are usually produced by halogen exchange starting from chlorinated methanes and ethanes. Illustrative is the synthesis of chlorodifluoromethane from chloroform:

HCCl3 + 2 HF → HCF2Cl + 2 HCl

The brominated derivatives are generated by free-radical reactions of the chlorofluorocarbons, replacing C-H bonds with C-Br bonds. The production of the anesthetic 2-bromo-2-chloro-1,1,1-trifluoroethane ("halothane") is illustrative:

CF3CH2Cl + Br2 → CF3CHBrCl + HBr


The most important reaction of the CFCs is the photo-induced scission of a C-Cl bond:

CCl3F → CCl2F. + Cl.

The chlorine atom, written often as Cl., behaves very differently from the chlorine molecule (Cl2). The radical Cl. is long-lived in the upper atmosphere, where it catalyzes the conversion of ozone into O2. Ozone absorbs UV-B radiation, so its depletion allows more of this high energy radiation to reach the Earth's surface. Bromine atoms are even more efficient catalysts; hence brominated CFCs are also regulated.


CFCs and HCFCs are used in a variety of applications because of their low toxicity, reactivity and flammability. Every permutation of fluorine, chlorine and hydrogen based on methane and ethane has been examined and most have been commercialized. Furthermore, many examples are known for higher numbers of carbon as well as related compounds containing bromine. Uses include refrigerants, blowing agents, propellants in medicinal applications and degreasing solvents.

Billions of kilograms of chlorodifluoromethane are produced annually as precursor to tetrafluoroethylene, the monomer that is converted into Teflon.[5]

Classes of compounds, nomenclature

  • Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CClmF4−m and C2ClmF6−m, where m is nonzero.
  • Hydro-chlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formula CClmFnH4−m−n and C2ClxFyH6−x−y, where m, n, x, and y are nonzero.
  • and bromofluorocarbons have formulae similar to the CFCs and HCFCs but also include bromine.
  • Hydrofluorocarbons (HFCs): when derived from methane, ethane, propane, and butane, these compounds have the respective formulae CFmH4−m, C2FmH6−m, C3FmH8−m, and C4FmH10−m, where m is nonzero.

Numbering system

A special numbering system is used for fluorinated alkanes, prefixed with Freon-, R-, CFC- and HCFC-, where the rightmost value indicates the number of fluorine atoms, the next value to the left is the number of hydrogen atoms plus 1, and the next value to the left is the number of carbon atoms less one (zeroes are not stated), and the remaining atoms are chlorine.

Freon-12, for example, indicates a methane derivative (only two numbers) containing two fluorine atoms (the second 2) and no hydrogen (1-1=0). It is therefore CCl2F2.

Another equation that can be applied to get the correct molecular formula of the CFC/R/Freon class compounds is this to take the numbering and add 90 to it. The resulting value will give the number of carbons as the first numeral, the second numeral gives the number of hydrogen atoms, and the third numeral gives the number of fluorine atoms. The rest of the unaccounted carbon bonds are occupied by chlorine atoms. The value of this equation is always a three figure number. An easy example is that of CFC-12, which gives: 90+12=102 -> 1 carbon, 0 hydrogens, 2 fluorine atoms, and hence 2 chlorine atoms resulting in CCl2F2. The main advantage of this method of deducing the molecular composition in comparison with the method described in the paragraph above is that it gives the number of carbon atoms of the molecule.

Freons containing bromine are signified by four numbers. Isomers, which are common for ethane and propane derivatives, are indicated by letters following the numbers :

Principal CFCs
Systematic name Common/trivial
name(s), code
Boiling point (°C) Formula
Trichlorofluoromethane Freon-11, R-11, CFC-11 23.77 CCl3F
Dichlorodifluoromethane Freon-12, R-12, CFC-12 −29.8 CCl2F2
Difluoromethane/pentafluoroethane R-410A, Puron, AZ-20 −48.5 50% CH2F2/50% CHF2CF3
Chlorotrifluoromethane Freon-13, R-13, CFC-13 −81 CClF3
Chlorodifluoromethane R-22, HCFC-22 −40.8 CHClF2
Dichlorofluoromethane R-21, HCFC-21 8.9 CHCl2F
Chlorofluoromethane Freon 31, R-31, HCFC-31 −9.1 CH2ClF
Bromochlorodifluoromethane BCF, Halon 1211, H-1211, Freon 12B1 −3.7 CBrClF2
1,1,2-Trichloro-1,2,2-trifluoroethane Freon 113, R-113, CFC-113, 1,1,2-Trichlorotrifluoroethane 47.7 Cl2FC-CClF2
1,1,1-Trichloro-2,2,2-trifluoroethane Freon 113a, R-113a, CFC-113a 45.9 Cl3C-CF3
1,2-Dichloro-1,1,2,2-tetrafluoroethane Freon 114, R-114, CFC-114, Dichlorotetrafluoroethane 3.8 ClF2C-CClF2
1-Chloro-1,1,2,2,2-pentafluoroethane Freon 115, R-115, CFC-115, Chloropentafluoroethane −38 ClF2C-CF3
2-Chloro-1,1,1,2-tetrafluoroethane R-124, HCFC-124 −12 CHFClCF3
1,1-Dichloro-1-fluoroethane R-141b, HCFC-141b 32 Cl2FC-CH3
1-Chloro-1,1-difluoroethane R-142b, HCFC-142b −9.2 ClF2C-CH3
Tetrachloro-1,2-difluoroethane Freon 112, R-112, CFC-112 91.5 CCl2FCCl2F
Tetrachloro-1,1-difluoroethane Freon 112a, R-112a, CFC-112a 91.5 CClF2CCl3
1,1,2-Trichlorotrifluoroethane Freon 113, R-113, CFC-113 48 CCl2FCClF2
1-bromo-2-chloro-1,1,2-trifluoroethane Halon 2311a 51.7 CHClFCBrF2
2-bromo-2-chloro-1,1,1-trifluoroethane Halon 2311 50.2 CF3CHBrCl
1,1-Dichloro-2,2,3,3,3-pentafluoropropane R-225ca, HCFC-225ca 51 CF3CF2CHCl2
1,3-Dichloro-1,2,2,3,3-pentafluoropropane R-225cb, HCFC-225cb 56 CClF2CF2CHClF


Carbon tetrachloride (CCl4) was used in fire extinguishers and glass "anti-fire grenades" from the late nineteenth century until around the end of World War II. Experimentation with chloroalkanes for fire suppression on military aircraft began at least as early as the 1920s. Freon is a trade name for a group of CFCs which are used primarily as refrigerants, but also have uses in fire-fighting and as propellants in aerosol cans. Bromomethane is widely used as a fumigant. Dichloromethane is a versatile industrial solvent.

The Belgian scientist Frédéric Swarts pioneered the synthesis of CFCs in the 1890s. He developed an effective exchange agent to replace chloride in carbon tetrachloride with fluoride to synthesize CFC-11 (CCl3F) and CFC-12 (CCl2F2).

In the late 1920s, Thomas Midgley, Jr. improved the process of synthesis and led the effort to use CFC as refrigerant to replace ammonia (NH3), chloromethane (CH3Cl), and sulfur dioxide (SO2), which are toxic but were in common use. In searching for a new refrigerant, requirements for the compound were: low boiling point, low toxicity, and to be generally non-reactive. In a demonstration for the American Chemical Society, Midgley flamboyantly demonstrated all these properties by inhaling a breath of the gas and using it to blow out a candle[6] in 1930.[7][8]

Commercial development and use


During World War II, various chloroalkanes were in standard use in military aircraft, although these early halons suffered from excessive toxicity. Nevertheless, after the war they slowly became more common in civil aviation as well. In the 1960s, fluoroalkanes and bromofluoroalkanes became available and were quickly recognized as being highly effective fire-fighting materials. Much early research with Halon 1301 was conducted under the auspices of the US Armed Forces, while Halon 1211 was, initially, mainly developed in the UK. By the late 1960s they were standard in many applications where water and dry-powder extinguishers posed a threat of damage to the protected property, including computer rooms, telecommunications switches, laboratories, museums and art collections. Beginning with warships, in the 1970s, bromofluoroalkanes also progressively came to be associated with rapid knockdown of severe fires in confined spaces with minimal risk to personnel.

By the early 1980s, bromofluoroalkanes were in common use on aircraft, ships, and large vehicles as well as in computer facilities and galleries. However, concern was beginning to be expressed about the impact of chloroalkanes and bromoalkanes on the ozone layer. The Vienna Convention for the Protection of the Ozone Layer did not cover bromofluoroalkanes as it was thought, at the time, that emergency discharge of extinguishing systems was too small in volume to produce a significant impact, and too important to human safety for restriction.


Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. After the development of his electron capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 60 ppt of CFC-11 over Ireland. In a self-funded research expedition ending in 1973, Lovelock went on to measure CFC-11 in both the Arctic and Antarctic, finding the presence of the gas in each of 50 air samples collected, and concluding that CFCs are not hazardous to the environment. The experiment did however provide the first useful data on the presence of CFCs in the atmosphere. The damage caused by CFCs was discovered by Sherry Rowland and Mario Molina who, after hearing a lecture on the subject of Lovelock's work, embarked on research resulting in the first publication suggesting the connection in 1974. It turns out that one of CFCs' most attractive features—their low reactivity— is key to their most destructive effects. CFCs' lack of reactivity gives them a lifespan that can exceed 100 years, giving them time to diffuse into the upper stratosphere.[9] Once in the stratosphere, the sun's ultraviolet radiation is strong enough to cause the homolytic cleavage of the C-Cl bond. In 1978, under the Toxic Substances Control Act, the EPA banned commercial manufacturing and use of CFCS and aerosol propellants. This was later superseded by broader regulation by the EPA under the Clean Air Act to address stratospheric ozone depletion[10].

Future ozone layer concentrations
NASA projection of stratospheric ozone, in Dobson units, if chlorofluorocarbons had not been banned. Animated version.

By 1987, in response to a dramatic seasonal depletion of the ozone layer over Antarctica, diplomats in Montreal forged a treaty, the Montreal Protocol, which called for drastic reductions in the production of CFCs. On 2 March 1989, 12 European Community nations agreed to ban the production of all CFCs by the end of the century. In 1990, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by the year 2000. By the year 2010, CFCs should have been completely eliminated from developing countries as well.

Ozone cfc trends
Ozone-depleting gas trends

Because the only CFCs available to countries adhering to the treaty is from recycling, their prices have increased considerably. A worldwide end to production should also terminate the smuggling of this material. However, there are current CFC smuggling issues, as recognized by the United Nations Environmental Programme (UNEP) in a 2006 report titled "Illegal Trade in Ozone Depleting Substances". UNEP estimates that between 16,000–38,000 tonnes of CFCs passed through the black market in the mid-1990s. The report estimated between 7,000 and 14,000 tonnes of CFCs are smuggled annually into developing countries. Asian countries are those with the most smuggling; as of 2007, China, India and South Korea were found to account for around 70% of global CFC production,[11] South Korea later to ban CFC production in 2010.[12] Possible reasons for continued CFC smuggling were also examined: the report noted that many banned CFC producing products have long lifespans and continue to operate. The cost of replacing the equipment of these items is sometimes cheaper than outfitting them with a more ozone-friendly appliance. Additionally, CFC smuggling is not considered a significant issue, so the perceived penalties for smuggling are low. In 2018 public attention was drawn to the issue, that at an unknown place in east Asia an estimated amount of 13.000 metric tons annually of CFCs have been produced since about 2012 in violation of the protocol.[13][14] While the eventual phaseout of CFCs is likely, efforts are being taken to stem these current non-compliance problems.

By the time of the Montreal Protocol, it was realised that deliberate and accidental discharges during system tests and maintenance accounted for substantially larger volumes than emergency discharges, and consequently halons were brought into the treaty, albeit with many exceptions.

Regulatory gap

While the production and consumption of CFCs are regulated under the Montreal Protocol, emissions from existing banks of CFCs are not regulated under the agreement. In 2002, there were an estimated 5,791 kilotons of CFCs in existing products such as refrigerators, air conditioners, aerosol cans and others.[15] Approximately one-third of these CFCs are projected to be emitted over the next decade if action is not taken, posing a threat to both the ozone layer and the climate.[16] A proportion of these CFCs can be safely captured and destroyed.

Regulation and DuPont

In 1978 the United States banned the use of CFCs such as Freon in aerosol cans, the beginning of a long series of regulatory actions against their use. The critical DuPont manufacturing patent for Freon ("Process for Fluorinating Halohydrocarbons", U.S. Patent #3258500) was set to expire in 1979. In conjunction with other industrial peers DuPont formed a lobbying group, the "Alliance for Responsible CFC Policy," to combat regulations of ozone-depleting compounds.[17] In 1986 DuPont, with new patents in hand, reversed its previous stance and publicly condemned CFCs.[18] DuPont representatives appeared before the Montreal Protocol urging that CFCs be banned worldwide and stated that their new HCFCs would meet the worldwide demand for refrigerants.[18]

Phasing-out of CFCs

Use of certain chloroalkanes as solvents for large scale application, such as dry cleaning, have been phased out, for example, by the IPPC directive on greenhouse gases in 1994 and by the volatile organic compounds (VOC) directive of the EU in 1997. Permitted chlorofluoroalkane uses are medicinal only.

Bromofluoroalkanes have been largely phased out and the possession of equipment for their use is prohibited in some countries like the Netherlands and Belgium, from 1 January 2004, based on the Montreal Protocol and guidelines of the European Union.

Production of new stocks ceased in most (probably all) countries in 1994. However many countries still require aircraft to be fitted with halon fire suppression systems because no safe and completely satisfactory alternative has been discovered for this application. There are also a few other, highly specialized uses. These programs recycle halon through "halon banks" coordinated by the Halon Recycling Corporation[19] to ensure that discharge to the atmosphere occurs only in a genuine emergency and to conserve remaining stocks.

The interim replacements for CFCs are hydrochlorofluorocarbons (HCFCs), which deplete stratospheric ozone, but to a much lesser extent than CFCs.[20] Ultimately, hydrofluorocarbons (HFCs) will replace HCFCs. Unlike CFCs and HCFCs, HFCs have an ozone depletion potential (ODP) of 0.[21] DuPont began producing hydrofluorocarbons as alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants.[22] Natural refrigerants are climate friendly solutions that are enjoying increasing support from large companies and governments interested in reducing global warming emissions from refrigeration and air conditioning. Hydrofluorocarbons are included in the Kyoto Protocol because of their very high Global Warming Potential and are facing calls to be regulated under the Montreal Protocol[23] due to the recognition of halocarbon contributions to climate change.[24]

On 21 September 2007, approximately 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely by 2020 in a United Nations-sponsored Montreal summit. Developing nations were given until 2030. Many nations, such as the United States and China, who had previously resisted such efforts, agreed with the accelerated phase out schedule.[25]

Development of alternatives for CFCs

Work on alternatives for chlorofluorocarbons in refrigerants began in the late 1970s after the first warnings of damage to stratospheric ozone were published.

The hydrochlorofluorocarbons (HCFCs) are less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer. Nevertheless, a significant fraction of the HCFCs do break down in the stratosphere and they have contributed to more chlorine buildup there than originally predicted. Later alternatives lacking the chlorine, the hydrofluorocarbons (HFCs) have an even shorter lifetimes in the lower atmosphere.[20] One of these compounds, HFC-134a, is now used in place of CFC-12 in automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane blend) are also used extensively in mobile air conditioning systems in Australia, the USA and many other countries, as they have excellent thermodynamic properties and perform particularly well in high ambient temperatures.

Among the natural refrigerants (along with ammonia and carbon dioxide), hydrocarbons have negligible environmental impacts and are also used worldwide in domestic and commercial refrigeration applications, and are becoming available in new split system air conditioners.[26] Various other solvents and methods have replaced the use of CFCs in laboratory analytics.[27]

In Metered-dose inhalers (MDI), a non-ozone effecting substitute was developed as a propellant, known as "hydrofluoroalkane."[28]

Applications and replacements for CFCs
Application Previously used CFC Replacement
Refrigeration & air-conditioning CFC-12 (CCl2F2); CFC-11(CCl3F); CFC-13(CClF3); HCFC-22 (CHClF2); CFC-113 (Cl2FCCClF2); CFC-114 (CClF2CClF2); CFC-115 (CF3CClF2); HFC-23 (CHF3); HFC-134a (CF3CFH2); HFC-507 (a 1:1 azeotropic mixture of HFC 125 (CF3 CHF2) and HFC-143a (CF3CH3)); HFC 410 (a 1:1 azeotropic mixture of HFC-32 (CF2H2) and HFC-125 (CF3CF2H))
Propellants in medicinal aerosols CFC-114 (CClF2CClF2) HFC-134a (CF3CFH2); HFC-227ea (CF3CHFCF3)
Blowing agents for foams CFC-11 (CCl3F); CFC 113 (Cl2FCCClF2); HCFC-141b (CCl2FCH3) HFC-245fa (CF3CH2CHF2); HFC-365 mfc (CF3CH2CF2CH3)
Solvents, degreasing agents, cleaning agents CFC-11 (CCl3F); CFC-113 (CCl2FCClF2) None

Environmental impacts

As previously discussed, CFCs were phased out via the Montreal Protocol due to their part in ozone depletion. However, the atmospheric impacts of CFCs are not limited to its role as an active ozone reducer. This anthropogenic compound is also a greenhouse gas, with a much higher potential to enhance the greenhouse effect than CO2.

Infrared absorption bands trap heat from escaping earth's atmosphere. In the case of CFCs, the strongest of these bands are located in the spectral region 7.8–15.3 µm [29] – referred to as an atmospheric window due to the relative transparency of the atmosphere within this region.[30] The strength of CFC bands and the unique susceptibility of the atmosphere, at which the compound absorbs and emits radiation, are two factors that contribute to CFCs' "super" greenhouse effect.[31] Another such factor is the low concentration of the compound. Because CO2 is close to saturation with high concentrations, it takes more of the substance to enhance the greenhouse effect. Conversely, the low concentration of CFCs allow their effects to increase linearly with mass.[31]

Tracer of ocean circulation

Because the time history of CFC concentrations in the atmosphere is relatively well known, they have provided an important constraint on ocean circulation. CFCs dissolve in seawater at the ocean surface and are subsequently transported into the ocean interior. Because CFCs are inert, their concentration in the ocean interior reflects simply the convolution of their atmospheric time evolution and ocean circulation and mixing.

CFC and SF6 tracer-derived age of ocean water

Chlorofluorocarbons (CFCs) are anthropogenic compounds that have been released into the atmosphere since the 1930s in various applications such as in air-conditioning, refrigeration, blowing agents in foams, insulations and packing materials, propellants in aerosol cans, and as solvents.[32] The entry of CFCs into the ocean makes them extremely useful as transient tracers to estimate rates and pathways of ocean circulation and mixing processes.[33] However, due to production restrictions of CFCs in the 1980s, atmospheric concentrations of CFC-11 and CFC-12 has stopped increasing, and the CFC-11 to CFC-12 ratio in the atmosphere have been steadily decreasing, making water dating of water masses more problematic.[33] Incidentally, production and release of sulfur hexafluoride (SF6) have rapidly increased in the atmosphere since the 1970s.[33] Similar to CFCs, SF6 is also an inert gas and is not affected by oceanic chemical or biological activities.[34] Thus, using CFCs in concert with SF6 as a tracer resolves the water dating issues due to decreased CFC concentrations.

Using CFCs or SF6 as a tracer of ocean circulation allows for the derivation of rates for ocean processes due to the time-dependent source function. The elapsed time since a subsurface water mass was last in contact with the atmosphere is the tracer-derived age.[35] Estimates of age can be derived based on the partial pressure of an individual compound and the ratio of the partial pressure of CFCs to each other (or SF6).[35]

Partial pressure and ratio dating techniques

The age of a water parcel can be estimated by the CFC partial pressure (pCFC) age or SF6 partial pressure (pSF6) age. The pCFC age of a water sample is defined as:

where [CFC] is the measured CFC concentration (pmol kg−1) and F is the solubility of CFC gas in seawater as a function of temperature and salinity.[36] The CFC partial pressure is expressed in units of 10–12 atmospheres or parts-per-trillion (ppt).[37] The solubility measurements of CFC-11 and CFC-12 have been previously measured by Warner and Weiss[37] Additionally, the solubility measurement of CFC-113 was measured by Bu and Warner[38] and SF6 by Wanninkhof et al.[39] and Bullister et al.[40] Theses authors mentioned above have expressed the solubility (F) at a total pressure of 1 atm as:

where F = solubility expressed in either mol l−1 or mol kg−1 atm−1, T = absolute temperature, S = salinity in parts per thousand (ppt), a1, a2, a3, b1, b2, and b3 are constants to be determined from the least squares fit to the solubility measurements.[38] This equation is derived from the integrated Van 't Hoff equation and the logarithmic Setchenow salinity dependence.[38]

It can be noted that the solubility of CFCs increase with decreasing temperature at approximately 1% per degree Celsius.[35]

Once the partial pressure of the CFC (or SF6) is derived, it is then compared to the atmospheric time histories for CFC-11, CFC-12, or SF6 in which the pCFC directly corresponds to the year with the same. The difference between the corresponding date and the collection date of the seawater sample is the average age for the water parcel.[35] The age of a parcel of water can also be calculated using the ratio of two CFC partial pressures or the ratio of the SF6 partial pressure to a CFC partial pressure.[35]


According to their material safety data sheets, CFCs and HCFCs are colorless, volatile, toxic liquids and gases with a faintly sweet ethereal odor. Overexposure at concentrations of 11% or more may cause dizziness, loss of concentration, central nervous system depression and/or cardiac arrhythmia. Vapors displace air and can cause asphyxiation in confined spaces. Although non-flammable, their combustion products include hydrofluoric acid, and related species.[41] Normal occupational exposure is rated at 0.07% and does not pose any serious health risks.[42]


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External links


Trichlorotrifluoroethane, also called 1,1,1-Trichloro-2,2,2-trifluoroethane or CFC-113a is a chlorofluorocarbon (CFC). It has the formula Cl3C-CF3.


Trichlorotrifluoroethane, also called 1,1,2-Trichloro-1,2,2-trifluoroethane or CFC-113 is a chlorofluorocarbon. It has the formula Cl2FC-CClF2. This colorless, volatile liquid is a versatile solvent. It has attracted much attention for its role in the depletion of stratospheric ozone. The amount of CFC-113 in the atmosphere has remained at about 80 parts per trillion, since the early 1990s. It is isomeric with 1,1,1-Trichloro-2,2,2-trifluoroethane, known as CFC-113a, which has the structural formula CF3-CCl3. The Montreal Protocol in 1987 called for the phase out of all CFC’s, including CFC-113 by 2010.


1,2-Dichlorotetrafluoroethane, or R-114, also known as cryofluorane (INN), is a chlorofluorocarbon (CFC) with the molecular formula ClF2CCF2Cl. Its primary use has been as a refrigerant. It is a non-flammable gas with a sweetish, chloroform-like odor with the critical point occurring at 145.6 °C and 3.26 MPa. When pressurized or cooled, it is a colorless liquid. It is listed on the Intergovernmental Panel on Climate Change's list of ozone depleting chemicals, and is classified as a Montreal Protocol Class I, group 1 ozone depleting substance.When used as a refrigerant, R-114 is classified as a medium pressure refrigerant.

The US Navy uses R-114 in its centrifugal chillers in preference to R-11 to avoid air and moisture leakage into the system. While the evaporator of an R-11 charged chiller runs at a vacuum during operation, R-114 yields approximately 0 psig operating pressure in the evaporator.


1-Chloro-3,3,3-trifluoropropene (HFO-1233zd) is the unsaturated chlorofluorocarbon with the formula HClC=C(H)CF3. This colorless gas is of interest as a refrigerant in air conditioners. The compound exists as E- and Z-isomers. It is prepared by fluorination and dehydrohalogenation reactions starting with 1,1,1,3,3-pentachloropropane.


Chloropentafluoroethane is a chlorofluorocarbon once used as a refrigerant. Its production and consumption has been banned since 1 January 1996 under the Montreal Protocol because of its ozone-depleting potential.


Chlorotrifluoroethylene (CTFE) is a chlorofluorocarbon with chemical formula CF2CClF. It is commonly used as a refrigerant in cryogenic applications. CTFE has a carbon-carbon double bond and so can be polymerized to form polychlorotrifluoroethylene or copolymerized to produce the plastic ECTFE. PCTFE has the trade name Neoflon PCTFE from Daikin Industries in Japan, and used to be produced under the trade name Kel-F from 3M Corporation in Minnesota.


Chlorotrifluoromethane, R-13, CFC-13, or Freon 13, is a non-flammable, non-corrosive chlorofluorocarbon (CFC) and also a mixed halomethane. It is used as a refrigerant, however, due to concerns about its ozone-depleting potential, its use has been phased out due to the Montreal Protocol.


Dichlorodifluoromethane (R-12) is a colorless gas usually sold under the brand name Freon-12, and a chlorofluorocarbon halomethane (CFC) used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in developed countries (non-article 5 countries) in 1996, and developing countries (article 5 countries) in 2010 due to concerns about its damaging impact to the ozone layer. Its only allowed usage is as fire retardant in submarines and aircraft. It is soluble in many organic solvents. Dichlorodifluoromethane was one of the original propellants for Silly String. R-12 cylinders are colored white. It is also known for smelling somewhat comparable to cannabis.

Frédéric Swarts

Frédéric Swarts (2 September 1866 – 6 September 1940) was a Belgian chemist who prepared the first chlorofluorocarbon, CF2Cl2 (Freon-12) as well as several other related compounds. He was a professor in the civil engineering at the University of Ghent. In addition to his work on organofluorine chemistry, he authored the textbook "Cours de Chimie Organique." He was a son of Theodore Swarts (chemist, *1839 Antwerpen; †1911 Kortenberg, Belgium) and a colleague of Leo Baekeland.

Giant Springs

Giant Springs is a large first magnitude spring located near Great Falls, Montana and is the central feature of Giant Springs State Park. Its water has a constant temperature of 54 °F (12 °C) and originates from snowmelt in the Little Belt Mountains, 60 miles (97 km) away. According to chlorofluorocarbon dating, the water takes about 3,000 years to travel underground before returning to the surface at the springs.

Giant Springs is formed by an opening in a part of the Madison aquifer, a vast aquifer underlying 5 U.S. States and 3 Canadian Provinces. The conduit between the mountains and the spring is the geological stratum found in parts of the northwest United States called the Madison Limestone. Although some of the underground water from the Little Belt Mountains escapes to form Giant Springs, some stays underground and continues flowing, joining sources from losing streams in the Black Hills, Big Horn Mountains and other areas. The aquifer eventually surfaces in Canada. Giant Springs has an average discharge of 242 cubic feet (6.9 m3) of water per second or 150 million gallons per day.

The spring outlet is located in Giant Springs State Park, just downstream and northeast of Great Falls, Montana on the east bank of the Missouri River. Giant Springs was first described by Lewis and Clark during their exploration of the Louisiana Purchase in 1805. Before that, the Blackfeet people utilized the springs as an easy-to-access water source in the winter. The springs were mostly ignored by settlers until 1884 when the town of Great Falls was established and the springs became the place for Sunday recreational activities. In the mid-1970s the park was established as a Montana State Park.Today, some of the spring water is bottled annually for human consumption and some of the discharge is used for a trout hatchery. The hatchery is a Montana state trout hatchery named Giant Springs Trout Hatchery and raises mostly Rainbow Trout. The spring serves as the headwaters of the 200-foot (61 m)-long Roe River, once listed as the shortest river in the world according to Guinness Book of World Records. The river flows into the Missouri River which is near the spring and borders its state park.

Greenhouse gas removal

Greenhouse gas removal projects are a type of climate engineering that seek to remove greenhouse gases from the atmosphere, and thus they tackle the root cause of global warming. These techniques either directly remove greenhouse gases, or alternatively seek to influence natural processes to remove greenhouse gases indirectly. The discipline overlaps with carbon capture and storage and carbon sequestration, and some projects listed may not be considered to be climate engineering by all commentators, instead being described as mitigation.

Ipratropium bromide/salbutamol

The combination preparation ipratropium bromide/salbutamol is a formulation containing ipratropium bromide (an anticholinergic) and salbutamol sulfate (albuterol sulfate, a β2-adrenergic receptor agonist) used in the management of chronic obstructive pulmonary disease (COPD) and asthma. It is marketed by Boehringer Ingelheim as a metered dose inhaler (MDI) and nebuliser under the trade name Combivent. It is also marketed by Dey, L.P. (Napa, California) under the brand name DuoNeb as a nebulizer. In Italy it is known as Breva. The chemical is sold in India by Cipla as duolin. Since Combivent contains a chlorofluorocarbon based propellant, it is being phased out in European Union countries. Chloroflourocarbons (CFC) are attributed to depletion of the ozone layer.

List of Cornell Manhattan Project people

Scientists from Cornell University played a major role in developing the technology that resulted in the first atomic bombs used in World War II. In turn, Cornell Physics professor Hans Bethe used the project as an opportunity to recruit young scientists to join the Cornell faculty after the war. The following people worked on the Manhattan Project primarily in Los Alamos, New Mexico during World War II and either studied or taught at Cornell University before or after the War:

Robert Fox Bacher – headed the experimental physics division, Cornell Physics professor from 1935 until the War

Manson Benedict – developed the gaseous diffusion method for separating the isotopes of uranium and supervised the engineering and process development of the K-25 plant in Oak Ridge, Tennessee, where fissionable material for the atomic bomb was produced

Hans Bethe – director of the theoretical division

Gertrude Blanch – oversaw calculations for the Manhattan Project

Oswald C. Brewster – Cornell class of 1918, project engineer who wrote to senior government officials warning about the potential of atomic bombs ending civilization.

Walter S. Carpenter, Jr. – oversaw the DuPont company's involvement in the Manhattan Project

Frederick J. Clarke – master's degree in civil engineering from Cornell University in 1940

Dale R. Corson – later became President of Cornell

John Curtin – Cornell theoretical physics Ph.D class of 1943

Jean Klein Dayton – helped design detonation systems

John W. DeWire – Cornell physics faculty

Richard Davisson – worked in Special Engineer Detachment

Eleanor & Richard Ehrlich

Richard Feynman – team leader under Bethe, later taught Physics at Cornell

Kenneth Greisen – worked on instrumentation, later Cornell Physics faculty

Lottie Grieff

William Higinbotham – headed the electronics group

Marshall Holloway – PhD from Cornell

Henry Hurwitz, Jr. – Cornell class of 1938

Walter Kauzmann – in charge of producing the detonator for the Trinity test

Margaret Ramsey Keck

Giovanni Rossi Lomanitz – worked at the Berkeley Radiation Laboratory; doctorate in theoretical physics from Cornell University, where he was the first graduate student of Richard Feynman.

Robert Marshak – PhD from Cornell University in 1939

Boyce McDaniel – later became director of Cornell's Laboratory of Nuclear Studies

William T. Miller – developed the chlorofluorocarbon polymer used in the first gaseous diffusion plant for the separation of uranium isotopes, Cornell chemistry faculty, 1936 – 1977

Elliott Waters Montroll – Head of the Mathematics Research Group at the Kellex Corporation in New York, working on programs associated with the Manhattan Project.

Philip Morrison – Cornell physics faculty 1946 – 1964.

Kenneth Nichols – deputy to General Leslie Groves, ME from Cornell

Paul Olum – later became President of the University of Oregon

Lyman G. Parrett – Cornell physics faculty

Arthur V. Peterson – Manhattan District's Chicago Area Engineer, responsible for the Metallurgical Laboratory

Edith Hinkley Quimby

Marcia White Rosenthal

Bruno Rossi – co-director of the Detector Group, Cornell physics faculty 1942-1946

Harvey L. Slatin – physicist and inventor who worked on the isolation of plutonium with the Special Engineering Detachment

LaRoy Thompson – Cornell class of 1942, physically assembled the first bomb and flew the practice bombing run at Bikini Island. Later, senior vice president and treasurer of the University of Rochester

Robert R. Wilson – head of the Cyclotron Group (R-1)

William M. Woodward – Cornell physics faculty

Mario J. Molina

Mario José Molina-Pasquel Henríquez (born March 19, 1943) is a Mexican-born American chemist known for his pivotal role in the discovery of the Antarctic ozone hole. He was a co-recipient of the 1995 Nobel Prize in Chemistry for his role in elucidating the threat to the Earth's ozone layer of chlorofluorocarbon gases (or CFCs). He became the first Mexican-born citizen to ever receive a Nobel Prize in Chemistry.In 2004 Molina accepted the positions of professor at the University of California, San Diego and the Center for Atmospheric Sciences at the Scripps Institution of Oceanography. Molina is also Director of the Mario Molina Center for Energy and Environment in Mexico City.

Molina is a climate policy adviser to President of Mexico, Enrique Peña Nieto.


PICO is an experiment searching for direct evidence of dark matter using a bubble chamber of chlorofluorocarbon (Freon) as the active mass. It is located at SNOLAB in Canada.

It was formed in 2013 from the merger of two similar experiments, PICASSO and COUPP.PICASSO (Project In CAnada to Search for Supersymmetric Objects, or Projet d'Identification de CAndidats Supersymétriques SOmbres in French) was an international collaboration with members from the Université de Montréal, Queen's University, Indiana University South Bend and Czech Technical University in Prague, University of Alberta, Laurentian University and BTI, Chalk River, Ontario. PICASSO is predominantly sensitive to spin-dependent interactions of Weakly Interacting Massive Particles (WIMPs) with fluorine atoms.

COUPP (Chicagoland Observatory for Underground Particle Physics) was a similar project with members from Fermilab, University of Chicago, and Indiana University. Prototypes were tested in the MINOS experiment far hall, with a scaled-up experiment also operating at SNOLAB. It used trifluoroiodomethane (CF3I) as the medium.


Pentachlorofluoroethane is a chlorofluorocarbon once used as a propellant and refrigerant. Its production and consumption has been banned since January 1, 1996 in developed countries, and January 1, 2010 in developing countries under the Montreal Protocol because of its ozone-depleting potential.

Susan Solomon

Susan Solomon (born January 19,1956 in Chicago) is an atmospheric chemist, working for most of her career at the National Oceanic and Atmospheric Administration. In 2011, Solomon joined the faculty at the Massachusetts Institute of Technology, where she serves as the Ellen Swallow Richards Professor of Atmospheric Chemistry & Climate Science. Solomon, with her colleagues, was the first to propose the chlorofluorocarbon free radical reaction mechanism that is the cause of the Antarctic ozone hole.Solomon is a member of the U.S. National Academy of Sciences, the European Academy of Sciences, and the French Academy of Sciences. In 2008, Solomon was selected by Time magazine as one of the 100 most influential people in the world. She also serves on the Science and Security Board for the Bulletin of the Atomic Scientists.


Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon. It is a colorless, faint ethereal, and sweetish-smelling liquid that boils around room temperature.

William T. Miller

William T. Miller (August 24, 1911 – November 15, 1998) was a professor of organic chemistry at Cornell University. His experimental research included investigations into the mechanism of addition of halogens, especially fluorine, to hydrocarbons. His work focused primarily on the physical and chemical properties of fluorocarbons and chlorofluorocarbons, and the synthesis of novel electrophilic reagents.

Miller carried out research into chemically resistant materials from which he developed the chlorofluorocarbon polymer used in K-25, the first gaseous diffusion plant constructed for the separation of uranium isotopes. The K-25 plant was a crucial factor in the development of "Little Boy" and other early nuclear weapons. Miller was also the first to synthesize methoxyflurane, a volatile inhalational anesthetic.

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