Chlorofluorocarbon

"CFCs" redirects here. For other singular uses, see CFC (disambiguation).

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propane.

The most common example is dichlorodifluoromethane (R-12). R-12 is also commonly called Freon and is used as a refrigerant. Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), gaseous fire suppression systems, and solvents. As a result of CFCs contributing 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) and Hydrofluoroolefins (HFOs)^[1] including R-410A,R-134a and R-1234yf.^[2][3][4]

Structure, properties and production

Main article: Organofluorine chemistry

As in simpler alkanes, carbon in the CFCs bond 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.^[5]

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

Brominated derivatives are generated by free-radical reactions of hydrochlorofluorocarbons, 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

Applications

CFCs and HCFCs are used in various applications because of their low toxicity, reactivity and flammability.^[6] 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, aerosol propellants in medicinal applications, and degreasing solvents.

Billions of kilograms of chlorodifluoromethane are produced annually as a precursor to tetrafluoroethylene, the monomer that is converted into Teflon.^[7]

Classes of compounds, nomenclature

• Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CCl_mF_4−m and C₂Cl_mF_6−m, where m is nonzero.
• Hydro-chlorofluorocarbons (HCFCs): when derived from methane and ethane these compounds have the formula CCl_mF_nH_4−m−n and C₂Cl_xF_yH_6−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 CF_mH_4−m, C₂F_mH_6−m, C₃F_mH_8−m, and C₄F_mH_10−m, where m is nonzero.

Numbering system

Main article: Refrigerant § Refrigerants by class and R-number

A special numbering system is to be 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
Chlorotrifluoromethane	Freon-13, R-13, CFC-13	−81	CClF3
Dichlorofluoromethane	R-21, HCFC-21	8.9	CHCl2F
Chlorodifluoromethane	R-22, HCFC-22	−40.8	CHClF2
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
1,1-Dichloro-1,2,2,2-tetrafluoroethane	CFC-114a	3.4	Cl2FC-CF3
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

Reactions

The most important reaction^{[citation needed]} 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.

Impact as greenhouse gases

 

The warming influence of greenhouse gases in the atmosphere has increased substantially in recent years. The rising presence of carbon dioxide from fossil fuel burning is the largest overall driver. The relatively smaller but significant warming impact from releases of the most abundantly produced CFCs (CFC11 and CFC12) will continue to persist for many further decades into the future.^[8][9]

CFCs were phased out via the Montreal Protocol due to their part in ozone depletion.

 

CFCs negatively affecting stratospheric ozone production

The atmospheric impacts of CFCs are not limited to their role as ozone-depleting chemicals. Infrared absorption bands prevent heat at that wavelength from escaping earth's atmosphere. CFCs have their strongest absorption bands from C-F and C-Cl bonds in the spectral region of 7.8–15.3 µm^[10]—referred to as the “atmospheric window” due to the relative transparency of the atmosphere within this region.^[11]

The strength of CFC absorption bands and the unique susceptibility of the atmosphere at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb radiation^[12] creates a “super” greenhouse effect from CFCs and other unreactive fluorine-containing gases such as perfluorocarbons, HFCs, HCFCs, bromofluorocarbons, SF₆, and NF₃.^[13] This “atmospheric window” absorption is intensified by the low concentration of each individual CFC. Because CO₂ is close to saturation with high concentrations and few infrared absorption bands, the radiation budget and hence the greenhouse effect has low sensitivity to changes in CO₂ concentration;^[14] the increase in temperature is roughly logarithmic.^[15] Conversely, the low concentration of CFCs allow their effects to increase linearly with mass,^[13] so that chlorofluorocarbons are greenhouse gases with a much higher potential to enhance the greenhouse effect than CO₂.

Groups are actively disposing of legacy CFCs to reduce their impact on the atmosphere.^[16]

According to NASA in 2018, the hole in the ozone layer has begun to recover as a result of CFC bans.^[17] However, new research released in 2023 reports an alarming increase in CFCs, pointing to unregulated use in China.^[18]

History

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 a 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^[19] in 1930.^[20][21]

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.

Regulation

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.^[22] Once in the stratosphere, the sun's ultraviolet radiation is strong enough to cause the homolytic cleavage of the C-Cl bond. In 1976, under the Toxic Substances Control Act, the EPA banned commercial manufacturing and use of CFCs and aerosol propellants. This was later superseded in the 1990 amendments to the Clean Air Act to address stratospheric ozone depletion.^[23]

 

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 2000. By 2010, CFCs should have been completely eliminated from developing countries as well.

 

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,^[24] South Korea later to ban CFC production in 2010.^[25] 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.^[26][27] 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.^[28] 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.^[29] 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.^[30] In 1986 DuPont, with new patents in hand, reversed its previous stance and publicly condemned CFCs.^[31] 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.^[31]

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.^{[citation needed]} 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^[32] 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.^[33] Ultimately, hydrofluorocarbons (HFCs) will replace HCFCs. Unlike CFCs and HCFCs, HFCs have an ozone depletion potential (ODP) of 0.^[34] DuPont began producing hydrofluorocarbons as alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants.^[35] 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.

Phasing-out of HFCs and HCFCs

Hydrofluorocarbons are included in the Kyoto Protocol and are regulated under the Kigali Amendment to the Montreal Protocol^[36] due to their very high Global Warming Potential and the recognition of halocarbon contributions to climate change.^[37]

On September 21, 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.^[38] India successfully phased out HCFCs by 2020.^[39]

Properly collecting, controlling, and destroying CFCs and HCFCs

While new production of these refrigerants has been banned, large volumes still exist in older systems and pose an immediate threat to our environment.^[40] Preventing the release of these harmful refrigerants has been ranked as one of the single most effective actions we can take to mitigate catastrophic climate change.^[41]

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.^[33] One of these compounds, HFC-134a, were used in place of CFC-12 in automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane blend) were also used extensively in mobile air conditioning systems in Australia, the US and many other countries, as they had excellent thermodynamic properties and performed particularly well in high ambient temperatures. 1,1-Dichloro-1-fluoroethane (HCFC-141b) has replaced HFC-134a, due to its low ODP and GWP values. And according to the Montreal Protocol, HCFC-141b is supposed to be phased out completely and replaced with zero ODP substances such as cyclopentane, HFOs, and HFC-345a before January 2020.^{[citation needed]}

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.^[42] Various other solvents and methods have replaced the use of CFCs in laboratory analytics.^[43]

In Metered-dose inhalers (MDI), a non-ozone effecting substitute was developed as a propellant, known as "hydrofluoroalkane."^[44]

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

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.^[45] 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.^[46] 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.^[46] Incidentally, production and release of sulfur hexafluoride (SF₆) have rapidly increased in the atmosphere since the 1970s.^[46] Similar to CFCs, SF₆ is also an inert gas and is not affected by oceanic chemical or biological activities.^[47] 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.^[48] 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).^[48]

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:

${\displaystyle pCFC={\frac {[CFC]}{F(T,S)}}}$ 

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.^[49] The CFC partial pressure is expressed in units of 10–12 atmospheres or parts-per-trillion (ppt).^[50] The solubility measurements of CFC-11 and CFC-12 have been previously measured by Warner and Weiss^[50] Additionally, the solubility measurement of CFC-113 was measured by Bu and Warner^[51] and SF₆ by Wanninkhof et al.^[52] and Bullister et al.^[53] Theses authors mentioned above have expressed the solubility (F) at a total pressure of 1 atm as:

${\displaystyle \ln F=a_{1}+a_{2}\left({\frac {100}{T}}\right)+a_{3}\ln \left({\frac {T}{100}}\right)+a_{4}\left({\frac {T}{100}}\right)^{2}+S\left[b_{1}+b_{2}\left({\frac {T}{100}}\right)+b_{3}\left({\frac {T}{100}}\right)\right],}$ 

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.^[51] This equation is derived from the integrated Van 't Hoff equation and the logarithmic Setchenow salinity dependence.^[51]

It can be noted that the solubility of CFCs increase with decreasing temperature at approximately 1% per degree Celsius.^[48]

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.^[48] 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.^[48]

Safety

According to their material safety data sheets, CFCs and HCFCs are colorless, volatile, non-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 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.^[54] Normal occupational exposure is rated at 0.07% and does not pose any serious health risks.^[55]

References

1. "Climate Change". The White House. 19 March 2021. from the original on 19 March 2021. Retrieved 11 April 2022.
2. Mironov, O. G. (1968). "Hydrocarbon pollution of the sea and its influence on marine organisms". Helgoländer Wissenschaftliche Meeresuntersuchungen. 17 (1–4): 335–339. Bibcode:1968HWM....17..335M. doi:10.1007/BF01611234.
3. Darby, Megan (19 August 2014). . rtcc.org. Archived from the original on 19 August 2014. Retrieved 11 April 2022.
4. https://www.gab-neumann.com/applications/$/Hydrofluoroolefins/201
5. Siegemund, Günter et al. (2002) "Fluorine Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a11_349
6. Plummer, L. Niel; Busenberg, Eurybiades (2000). "Chlorofluorocarbons". Environmental Tracers in Subsurface Hydrology. pp. 441–478. doi:10.1007/978-1-4615-4557-6_15. ISBN 978-1-4613-7057-4.
7. Rossberg, M. et al. (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
8. "The NOAA Annual Greenhouse Gas Index (AGGI)". NOAA.gov. National Oceanographic and Atmospheric Administration (NOAA). Spring 2023. from the original on 24 May 2023.
9. "Appendix 8.A" (PDF). Intergovernmental Panel on Climate Change Fifth Assessment Report. p. 731. (PDF) from the original on 2017-10-13. Retrieved 2020-07-15.
10. Rothman, L; Gordon, I.E.; Barbe, A.; Benner, D.Chris; Bernath, P.F.; Birk, M.; Boudon, V.; Brown, L.R.; Campargue, A.; Champion, J.-P.; Chance, K.; Coudert, L.H.; Dana, V.; Devi, V.M.; Fally, S.; Flaud, J.-M.; Gamache, R.R.; Goldman, A.; Jacquemart, D.; Kleiner, I.; Lacome, N.; Lafferty, W.J.; Mandin, J.-Y.; Massie, S.T.; Mikhailenko, S.N.; Miller, C.E.; Moazzen-Ahmadi, N.; Naumenko, O.V.; Nikitin, A.V.; et al. (2009). "The HITRAN 2008 molecular spectroscopic database" (PDF). Journal of Quantitative Spectroscopy and Radiative Transfer. 100 (9–10): 533–572. Bibcode:2009JQSRT.110..533R. doi:10.1016/j.jqsrt.2009.02.013. (PDF) from the original on 2015-04-03.
11. Ramanathan, V (1975). "Greenhouse Effect Due to Chlorofluorocarbons: Climatic Implications". Science. New Series. 190 (4209): 50–52. Bibcode:1975Sci...190...50R. doi:10.1126/science.190.4209.50. JSTOR 1740877. S2CID 33736550.
12. Bera, Partha P.; Francisco, Joseph S. and Lee, Timothy J.; ‘Identifying the Molecular Origin of Global Warming’; Journal of Physical Chemistry; 113 (2009), pp. 12694-12699
13. Ramanathan, V; Y. Feng (2009). "Air pollution, greenhouse gases and climate change: Global and regional perspectives". Atmospheric Environment. 43 (1): 37–50. Bibcode:2009AtmEn..43...37R. doi:10.1016/j.atmosenv.2008.09.063.
14. Harnung, Sven E. and Johnson, Matthew S.; Chemistry and the Environment, p. 365 ISBN 1107021553
15. Röhl, C.M.; Boğlu, D.; Brtihl, C. and Moortgat, G. K.; ‘Infrared band intensities and global warming potentials of CF₄, C₂F₆, C₃F₈, C₄F₁₀, C₅F₁₂, and C₆F₁₄’; Geophysical Research Letters; vol. 22, no. 7 (1995), pp. 815-818
16. "One overlooked way to fight climate change? Dispose of old CFCs". Environment. 2019-04-29. from the original on 2019-04-29. Retrieved 2019-04-30.
17. Samson Reiny (4 January 2018). "NASA Study: First Direct Proof of Ozone Hole Recovery Due to Chemicals Ban". NASA. from the original on 24 September 2020. Retrieved 2 October 2019.
18. CFC use in China
19. Bellis, Mary (12 August 2016). "Where Does Freon Come From?". ThoughtCo. Retrieved 11 April 2022.
20. Carlisle, Rodney (2004). Scientific American inventions and discoveries : all the milestones in ingenuity--from the discovery of fire to the invention of the microwave oven. Hoboken, N.J: John Wiley & Sons. p. 351. ISBN 0-471-24410-4. OCLC 53284995.
21. McNeill, J.R. (2001). Something New Under the Sun: An Environmental History of the Twentieth-Century World (The Global Century Series). The Global Century Series. W. W. Norton. p. 421. ISBN 978-0-393-32183-8. Retrieved 11 April 2022. (as reviewed in the Journal of Political Ecology 2004-03-28 at the Wayback Machine)
22. Lee, Bing-Sun; Chiou, Chung-Biau (October 2008). "The Relationship of Meteorological and Anthropogenic Factors to Time Series Measurements of CFC-11, CFC-12, and CH3CCl3 Concentrations in the Urban Atmosphere". Atmospheric Environment. 42 (33): 7707. Bibcode:2008AtmEn..42.7706L. doi:10.1016/j.atmosenv.2008.05.042.
23. Auer, Charles, Frank Kover, James Aidala, Marks Greenwood. “Toxic Substances: A Half Century of Progress.” 2021-07-02 at the Wayback Machine EPA Alumni Association. March 2016.
24. "Illegal Trade in Ozone Depleting Substances" 2012-03-22 at the Wayback Machine. United Nations Environmental Programme. 2007. Web. 3 April 2011.
25. S. Korea to ban import, production of freon, halon gases in 2010 2014-08-10 at the Wayback Machine. Yonhap News Agency. 23 December 2009
26. "Ozonkiller: Ein verbotener Stoff in der Atmosphäre - WELT". Welt.de (in German). 16 May 2018. from the original on 2020-10-05. Retrieved 2018-05-18.
27. "Ozone hole-forming chemical emissions increasing and mysterious source in East Asia may be responsible". Independent.co.uk. 16 May 2018. from the original on 2020-11-09. Retrieved 2018-05-18.
28. Campbell, Nick et al. , Ch. 11 in IPCC/TEAP Special Report: Safeguarding the Ozone Layer and the Global Climate System
29. Chlorofluorocarbons: An Overlooked Climate Threat, EESI Congressional Briefing 2009-12-04 at the Wayback Machine. Eesi.org. Retrieved on 24 September 2011.
30. Desombre, E.R., 2000: Domestic Sources of International Environmental Policy: Industry, Environmentalists, and U.S. Power. MIT Press. SBN: 9780262041799. p. 93.
31. "Ethics of Du Pont's CFC Strategy 1975–1995", Smith B. Journal of Business Ethics, Volume 17, Number 5, April 1998, pp. 557–568(12)
32. Welcome to the Halon Corporation 2009-09-19 at the Wayback Machine. Halon.org. Retrieved on 24 September 2011.
33. Prinn, R. G.; Weiss, R. F.; Fraser, P. J.; Simmonds, P. G.; Cunnold, D. M.; Alyea, F. N.; O'Doherty, S.; Salameh, P.; Miller, B. R.; Huang, J.; Wang, R. H. J.; Hartley, D. E.; Harth, C.; Steele, L. P.; Sturrock, G.; Midgley, P. M.; McCulloch, A. (27 July 2000). "A History of Chemically and Radiatively Important Gases in Air Deduced from ALE/GAGE/AGAGE". Journal of Geophysical Research: Atmospheres. 105 (D14): 17751–17792. Bibcode:2000JGR...10517751P. doi:10.1029/2000JD900141. ISSN 2156-2202.
34. "Ozone Layer Depletion", U.S. Environmental Protection Agency 2008-09-19 at the Wayback Machine accessed 25 June 2008
35. Freon® : 1930. In Depth 2011-03-19 at the Wayback Machine. dupont.com (30 January 2009). Retrieved on 2011-09-24.
36. Broder, John M. (9 November 2010). "A Novel Tactic in Climate Fight Gains Some Traction". The New York Times. p. A9. from the original on 20 May 2013. Retrieved 5 February 2013.
37. Velders, G. J. M.; Andersen, S. O.; Daniel, J. S.; Fahey, D. W.; McFarland, M. (2007). "The importance of the Montreal Protocol in protecting climate". Proceedings of the National Academy of Sciences. 104 (12): 4814–9. Bibcode:2007PNAS..104.4814V. doi:10.1073/pnas.0610328104. PMC 1817831. PMID 17360370.
38. HCFC Phaseout Schedule 2009-07-16 at the Wayback Machine. Epa.gov (28 June 2006). Retrieved on 2011-09-24.
39. "India achieves complete phase out of one the most potent ozone depleting chemical". pib.gov.in. Retrieved 2022-06-02.
40. "Emissions of several ozone-depleting chemicals are larger than expected". MIT News | Massachusetts Institute of Technology. 17 March 2020. Retrieved 2022-10-18.
41. "Refrigerant Management @ProjectDrawdown #ClimateSolutions". Project Drawdown. 2020-02-06. Retrieved 2022-10-18.
42. "Greenpeace, Cool Technologies" 2008-07-06 at the Wayback Machine. (PDF). Retrieved on 24 September 2011.
43. Use of Ozone Depleting Substances in Laboratories. TemaNord 516/2003 February 27, 2008, at the Wayback Machine. Norden.org (1 January 2003). Retrieved on 2011-09-24.
44. Boccuzzi, S. J; Wogen, J; Roehm, J. B (2000). "Use of hydrofluoroalkane propellant delivery system for inhaled albuterol in patients receiving asthma medications". Clinical Therapeutics. 22 (2): 237–47. doi:10.1016/S0149-2918(00)88482-9. PMID 10743983.
45. Plummer LN and Busenberg E. (2006). "Chlorofluorocarbons in aquatic environments", Ch. 1, pp. 1–8. In IAEA (ed.), Use of chlorofluorocarbons in hydrology – A guidebook 2016-04-15 at the Wayback Machine: Vienna, International Atomic Energy Agency.
46. Bullister, J. L.; Wisegarver, D. P. (2008). "The shipboard analysis of trace levels of sulfur hexafluoride, chlorofluorocarbon-11 and chlorofluorocarbon-12 in seawater". Deep-Sea Research Part I: Oceanographic Research Papers. 55 (8): 1063–1074. Bibcode:2008DSRI...55.1063B. doi:10.1016/j.dsr.2008.03.014. from the original on 2020-07-28. Retrieved 2020-04-30.
47. Watanabe, Y. W.; Shimamoto, A.; Ono, T. (2003). "Comparison of Time-Dependent Tracer Ages in the Western North Pacific: Oceanic Background Levels of SF₆, CFC-11, CFC-12 and CFC-113". Journal of Oceanography. 59 (5): 719–729. doi:10.1023/B:JOCE.0000009600.12070.1a. S2CID 129791859. from the original on 2021-11-22. Retrieved 2017-11-03.
48. Fine, Rana A. (2011). (PDF). Annual Review of Marine Science. 3 (1): 173–95. Bibcode:2011ARMS....3..173F. doi:10.1146/annurev.marine.010908.163933. PMID 21329203. Archived from the original (PDF) on 2015-02-10. Retrieved 2015-01-31.
49. Warner, M. J.; Weiss, R. F. (1985). "Solubilities of chlorofluorocarbons 11 and 12 in water and seawater". Deep-Sea Research Part A: Oceanographic Research Papers. 32 (12): 1485–1497. Bibcode:1985DSRA...32.1485W. doi:10.1016/0198-0149(85)90099-8.
50. Min, D. H.; Warner, M. J.; Bullister, J. L. (2010). "Estimated rates of carbon tetrachloride removal in the thermocline and deep waters of the East Sea (Sea of Japan)". Marine Chemistry. 121 (1–4): 100–111. Bibcode:2010MarCh.121..100M. doi:10.1016/j.marchem.2010.03.008.
51. Bu, X.; Warner, M. J. (1995). "Solubility of chlorofluorocarbon 113 in water and seawater". Deep-Sea Research Part I: Oceanographic Research Papers. 42 (7): 1151–1161. Bibcode:1995DSRI...42.1151B. doi:10.1016/0967-0637(95)00052-8.
52. Wanninkhof, R.; Ledwell, J. R.; Watson, A. J. (1991). "Analysis of sulfur hexafluoride in seawater". Journal of Geophysical Research. 96 (C5): 8733. Bibcode:1991JGR....96.8733W. doi:10.1029/91JC00104.
53. Bullister, J. L.; Wisegarver, D. P.; Menzia, F. A. (2002). "The solubility of sulfur hexafluoride in water and seawater". Deep-Sea Research Part I: Oceanographic Research Papers. 49 (1): 175–187. Bibcode:2002DSRI...49..175B. doi:10.1016/S0967-0637(01)00051-6. from the original on 2015-09-24.
54. Material Safety Data Sheet 2011-02-08 at the Wayback Machine. National Refrigerants
55. WHO. "Fully Halogenated Chlorofluorocarbons". International Programme on Chemical Safety. from the original on 2012-05-05.

External links

• Gas conversion table
• Nomenclature FAQ
• Numbering scheme for Ozone-Depleting Substances and their substitutes
• Class I Ozone-Depleting Substances
• Class II Ozone-Depleting Substances (HCFCs)
• CFC illegal trade
• History of halon-use by the US Navy 2000-08-19 at the Wayback Machine
• Ozone Loss: The Chemical Culprits
• Process using pyrolysis in an ultra high temperature plasma arc, for the elimination of CFCs 2016-04-15 at the Wayback Machine
• [1] Environmental Investigation Agency: Reports etc. on illegal trade and solutions
• [2] Environmental Investigation Agency in the USA: Reports etc. on illegal trade and solutions
• [3] Phasing out halons in extinguishers