In 1978 the United States Banned the Use of Cfcs Legislation Voted Agains

Grade of organic compounds commonly used equally refrigerants

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that comprise carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced every bit volatile derivatives of methyl hydride, ethane, and propane. They are also ordinarily known past 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 temper, the manufacture of such compounds has been phased out nether the Montreal Protocol, and they are beingness replaced with other products such as hydrofluorocarbons (HFCs)^[1] including R-410A and R-134a.^{[two] [iii]}

Structure, properties and production [edit]

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

The concrete properties of CFCs and HCFCs are tunable past changes in the number and identity of the halogen atoms. In full general, they are volatile merely less so than their parent alkanes. The decreased volatility is attributed to the molecular polarity induced past the halides, which induces intermolecular interactions. Thus, methane boils at −161 °C whereas the fluoromethanes boil between −51.7 (CF₂H₂) and −128 °C (CF_four). The CFCs have notwithstanding higher boiling points because the chloride is even more than polarizable than fluoride. Because of their polarity, the CFCs are useful solvents, and their humid points brand them suitable equally refrigerants. The CFCs are far less flammable than marsh gas, in part because they incorporate fewer C-H bonds and in role because, in the instance 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 ordinarily produced past halogen exchange starting from chlorinated methanes and ethanes. Illustrative is the synthesis of chlorodifluoromethane from chloroform:

HCCl_three + 2 HF → HCF₂Cl + 2 HCl

Brominated derivatives are generated by complimentary-radical reactions of hydrochlorofluorocarbons, replacing C-H bonds with C-Br bonds. The production of the anesthetic 2-bromo-2-chloro-ane,one,one-trifluoroethane ("halothane") is illustrative:

CF₃CH_iiCl + Br_ii → CF₃CHBrCl + HBr

Applications [edit]

CFCs and HCFCs are used in various 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 accept been commercialized. Furthermore, many examples are known for higher numbers of carbon besides equally 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 equally a precursor to tetrafluoroethylene, the monomer that is converted into Teflon.^[5]

Classes of compounds, nomenclature [edit]

• Chlorofluorocarbons (CFCs): when derived from methane and ethane these compounds have the formulae CCl₁₀₀₀F_4−m and C₂Cl_thouF_6−m, where yard is nonzero.
• Hydro-chlorofluorocarbons (HCFCs): when derived from marsh gas and ethane these compounds have the formula CCl_grandF_nH_4−m−n and C₂Cl_xF_yH_6−ten−y, where m, north, x, and y are nonzero.
• and bromofluorocarbons have formulae similar to the CFCs and HCFCs just also include bromine.
• Hydrofluorocarbons (HFCs): when derived from methane, ethane, propane, and butane, these compounds accept the corresponding formulae CF_mH_4−g, C₂F_mH_{half dozen−k}, C₃F_mH_8−m, and C₄F_yardH_10−m, where m is nonzero.

Numbering arrangement [edit]

A special numbering organization is to be used for fluorinated alkanes, prefixed with Freon-, R-, Chlorofluorocarbon- and HCFC-, where the rightmost value indicates the number of fluorine atoms, the side by side value to the left is the number of hydrogen atoms plus 1, and the adjacent value to the left is the number of carbon atoms less 1 (zeroes are non 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.

Some other equation that can exist practical to get the correct molecular formula of the CFC/R/Freon class compounds is this to take the numbering and add together 90 to it. The resulting value will give the number of carbons every bit the first numeral, the second numeral gives the number of hydrogen atoms, and the third numeral gives the number of fluorine atoms. The remainder 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 -> i carbon, 0 hydrogens, two fluorine atoms, and hence 2 chlorine atoms resulting in CCl_twoF_two. The chief 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 past messages following the numbers :

Principal CFCs
Systematic proper noun	Mutual/trivial name(s), code	Boiling point (°C)	Formula
Trichlorofluoromethane	Freon-xi, R-eleven, CFC-xi	23.77	CCliiiF
Dichlorodifluoromethane	Freon-12, R-12, CFC-12	−29.eight	CCl2Ftwo
Chlorotrifluoromethane	Freon-13, R-thirteen, CFC-13	−81	CClFthree
Dichlorofluoromethane	R-21, HCFC-21	eight.nine	CHCl2F
Chlorodifluoromethane	R-22, HCFC-22	−40.eight	CHClFtwo
Chlorofluoromethane	Freon 31, R-31, HCFC-31	−9.1	CH2ClF
Bromochlorodifluoromethane	BCF, Halon 1211, H-1211, Freon 12B1	−3.7	CBrClF2
1,1,ii-Trichloro-one,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
one,2-Dichloro-one,ane,2,2-tetrafluoroethane	Freon 114, R-114, Chlorofluorocarbon-114, Dichlorotetrafluoroethane	three.viii	ClF2C-CClF2
i-Chloro-1,1,two,2,2-pentafluoroethane	Freon 115, R-115, Cfc-115, Chloropentafluoroethane	−38	ClFtwoC-CF3
ii-Chloro-1,1,1,2-tetrafluoroethane	R-124, HCFC-124	−12	CHFClCF3
1,one-Dichloro-1-fluoroethane	R-141b, HCFC-141b	32	Cl2FC-CH3
ane-Chloro-1,1-difluoroethane	R-142b, HCFC-142b	−9.2	ClF2C-CHiii
Tetrachloro-1,2-difluoroethane	Freon 112, R-112, Chlorofluorocarbon-112	91.5	CCl2FCCltwoF
Tetrachloro-1,one-difluoroethane	Freon 112a, R-112a, CFC-112a	91.five	CClF2CCl3
1,1,2-Trichlorotrifluoroethane	Freon 113, R-113, Cfc-113	48	CCliiFCClFii
1-bromo-2-chloro-one,1,two-trifluoroethane	Halon 2311a	51.7	CHClFCBrF2
2-bromo-2-chloro-1,1,1-trifluoroethane	Halon 2311	l.two	CF3CHBrCl
1,ane-Dichloro-ii,two,iii,3,3-pentafluoropropane	R-225ca, HCFC-225ca	51	CF3CF2CHCltwo
i,three-Dichloro-1,2,2,3,3-pentafluoropropane	R-225cb, HCFC-225cb	56	CClFtwoCFiiCHClF

Reactions [edit]

The most important reaction^{[ commendation needed ]} of the CFCs is the photo-induced scission of a C-Cl bond:

CCl₃F → CCl_twoF ^. + Cl ^.

The chlorine atom, written ofttimes as Cl ^. , behaves very differently from the chlorine molecule (Cl_ii). 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 than of this high free energy radiation to reach the Earth'south surface. Bromine atoms are even more than efficient catalysts; hence brominated CFCs are also regulated.

Impact as greenhouse gases [edit]

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 touch from releases of the nigh abundantly produced CFCs (CFC11 and CFC12) volition continue to persist for many further decades into the future.^[6]

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

The atmospheric impacts of CFCs are not limited to their function equally ozone-depleting chemicals. Infrared absorption bands foreclose heat at that wavelength from escaping world's temper. CFCs take their strongest absorption bands from C-F and C-Cl bonds in the spectral region of 7.eight–fifteen.3 µm^[7]—referred to equally the "atmospheric window" due to the relative transparency of the atmosphere within this region.^[8]

The strength of Cfc absorption bands and the unique susceptibility of the temper at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb radiations^[9] creates a "super" greenhouse effect from CFCs and other unreactive fluorine-containing gases such equally perfluorocarbons, HFCs, HCFCs, bromofluorocarbons, SF_vi, and NF_iii.^[10] 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 upkeep and hence the greenhouse effect has depression sensitivity to changes in CO_two concentration;^[eleven] the increment in temperature is roughly logarithmic.^[12] Conversely, the low concentration of CFCs allow their effects to increase linearly with mass,^[10] and then that chlorofluorocarbons are greenhouse gases with a much higher potential to heighten the greenhouse issue than CO₂.

Groups are actively disposing of legacy CFCs to reduce their touch on the atmosphere.^[13]

According to NASA in 2018, the pigsty in the ozone layer has begun to recover every bit a result of Cfc bans.^[fourteen]

History [edit]

Carbon tetrachloride (CCl_iv) was used in fire extinguishers and glass "anti-fire grenades" from the late nineteenth century until around the finish of World State of war Two. Experimentation with chloroalkanes for fire suppression on military aircraft began at least as early on as the 1920s. Freon is a trade name for a grouping of CFCs which are used primarily as refrigerants, but too take uses in burn down-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 adult an effective exchange agent to replace chloride in carbon tetrachloride with fluoride to synthesize Chlorofluorocarbon-11 (CCl_threeF) and Chlorofluorocarbon-12 (CCl_twoF₂).

In the tardily 1920s, Thomas Midgley Jr. improved the process of synthesis and led the effort to use CFC equally a refrigerant to replace ammonia (NH_three), chloromethane (CH₃Cl), and sulfur dioxide (And then_ii), which are toxic but were in mutual 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^[fifteen] in 1930.^{[xvi] [17]}

Commercial development and use [edit]

During Earth War 2, diverse chloroalkanes were in standard use in military aircraft, although these early on halons suffered from excessive toxicity. Withal, subsequently the state of war they slowly became more common in civil aviation as well. In the 1960s, fluoroalkanes and bromofluoroalkanes became available and were rapidly recognized every bit being highly effective burn down-fighting materials. Much early on enquiry with Halon 1301 was conducted nether the auspices of the The states Military, 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 harm 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 bars spaces with minimal risk to personnel.

Past the early 1980s, bromofluoroalkanes were in common utilise on shipping, ships, and large vehicles as well as in computer facilities and galleries. However, concern was get-go 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 non cover bromofluoroalkanes equally it was thought, at the time, that emergency discharge of extinguishing systems was too small in volume to produce a meaning impact, and as well important to human condom for brake.

Regulation [edit]

Since the tardily 1970s, the use of CFCs has been heavily regulated because of their destructive furnishings on the ozone layer. After the evolution 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 Chlorofluorocarbon-eleven over Republic of ireland. In a self-funded inquiry 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 acquired 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 subversive effects. CFCs' lack of reactivity gives them a lifespan that can exceed 100 years, giving them time to diffuse into the upper stratosphere.^[xviii] Once in the stratosphere, the sun's ultraviolet radiations is stiff plenty to cause the homolytic cleavage of the C-Cl bail. In 1976, under the Toxic Substances Command 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 accost stratospheric ozone depletion.^[19]

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 consummate 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 bachelor to countries adhering to the treaty is from recycling, their prices have increased considerably. A worldwide end to production should also end the smuggling of this textile. However, there are electric current Cfc smuggling issues, as recognized by the Un Environmental Plan (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 seven,000 and 14,000 tonnes of CFCs are smuggled annually into developing countries. Asian countries are those with the well-nigh smuggling; as of 2007, China, Republic of india and South Korea were found to account for around lxx% of global CFC production,^[twenty] Republic of korea later on to ban CFC production in 2010.^[21] Possible reasons for continued CFC smuggling were also examined: the report noted that many banned Chlorofluorocarbon 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, Chlorofluorocarbon smuggling is not considered a significant upshot, so the perceived penalties for smuggling are low. In 2018 public attention was drawn to the issue, that at an unknown place in e Asia an estimated amount of 13,000 metric tons annually of CFCs take been produced since about 2012 in violation of the protocol.^{[22] [23]} While the eventual phaseout of CFCs is likely, efforts are being taken to stalk these current non-compliance problems.

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

Regulatory gap [edit]

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 five,791 kilotons of CFCs in existing products such as refrigerators, air conditioners, aerosol cans and others.^[24] Approximately ane-3rd of these CFCs are projected to exist emitted over the next decade if action is not taken, posing a threat to both the ozone layer and the climate.^[25] A proportion of these CFCs can be safely captured and destroyed.

Regulation and DuPont [edit]

In 1978 the The states banned the use of CFCs such as Freon in droplets cans, the starting time of a long series of regulatory actions against their utilise. 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 grouping, the "Brotherhood for Responsible Cfc Policy," to combat regulations of ozone-depleting compounds.^[26] In 1986 DuPont, with new patents in hand, reversed its previous stance and publicly condemned CFCs.^[27] DuPont representatives appeared before the Montreal Protocol urging that CFCs exist banned worldwide and stated that their new HCFCs would see the worldwide demand for refrigerants.^[27]

Phasing-out of CFCs [edit]

Use of certain chloroalkanes as solvents for large calibration application, such equally 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 holland and Belgium, from 1 January 2004, based on the Montreal Protocol and guidelines of the European Union.

Production of new stocks ceased in virtually (probably all) countries in 1994.^{[ citation needed ]} However many countries still require aircraft to be fitted with halon fire suppression systems because no rubber 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 past the Halon Recycling Corporation^[28] 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.^[29] Ultimately, hydrofluorocarbons (HFCs) will supervene upon HCFCs. Different CFCs and HCFCs, HFCs accept an ozone depletion potential (ODP) of 0.^[30] DuPont began producing hydrofluorocarbons equally alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants.^[31] 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 [edit]

Hydrofluorocarbons are included in the Kyoto Protocol and are regulated under the Kigali Amendment to the Montreal Protocol^[32] due to their very high Global Warming Potential and the recognition of halocarbon contributions to climate change.^[33]

On September 21, 2007, approximately 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely past 2020 in a United Nations-sponsored Montreal meridian. 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.^[34]

Development of alternatives for CFCs [edit]

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. Yet, a significant fraction of the HCFCs do intermission down in the stratosphere and they have contributed to more chlorine buildup in that location than originally predicted. Later alternatives defective the chlorine, the hydrofluorocarbons (HFCs) take an even shorter lifetimes in the lower atmosphere.^[29] One of these compounds, HFC-134a, were used in place of CFC-12 in automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane alloy) were likewise used extensively in mobile air conditioning systems in Australia, the US and many other countries, as they had first-class thermodynamic properties and performed particularly well in high ambience 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 zip ODP substances such equally cyclopentane, HFOs, and HFC-345a earlier Jan 2020.^{[ citation needed ]}

Amid the natural refrigerants (along with ammonia and carbon dioxide), hydrocarbons take negligible environmental impacts and are also used worldwide in domestic and commercial refrigeration applications, and are condign available in new split system air conditioners.^[35] Various other solvents and methods have replaced the utilize of CFCs in laboratory analytics.^[36]

In Metered-dose inhalers (MDI), a non-ozone effecting substitute was developed as a propellant, known as "hydrofluoroalkane."^[37]

Applications and replacements for CFCs
Application	Previously used Cfc	Replacement
Refrigeration & air-conditioning	CFC-12 (CCl2F2); CFC-xi(CCl3F); Cfc-13(CClF3); HCFC-22 (CHClFtwo); Chlorofluorocarbon-113 (Cl2FCCClF2); Cfc-114 (CClFiiCClF2); CFC-115 (CFthreeCClF2);	HFC-23 (CHF3); HFC-134a (CF3CFH2); HFC-507 (a ane:1 azeotropic mixture of HFC 125 (CFthree CHF2) and HFC-143a (CF3CH3)); HFC 410 (a ane:1 azeotropic mixture of HFC-32 (CFiiH2) and HFC-125 (CF3CFtwoH))
Propellants in medicinal aerosols	Chlorofluorocarbon-114 (CClFiiCClF2)	HFC-134a (CF3CFH2); HFC-227ea (CF3CHFCF3)
Bravado agents for foams	CFC-11 (CCl3F); Cfc 113 (CltwoFCCClFii); HCFC-141b (CCl2FCH3)	HFC-245fa (CF3CHiiCHF2); HFC-365 mfc (CFthreeCH2CFtwoCH3)
Solvents, degreasing agents, cleaning agents	CFC-xi (CCliiiF); CFC-113 (CCliiFCClF2)	None

Tracer of ocean circulation [edit]

Because the fourth dimension history of Cfc concentrations in the atmosphere is relatively well known, they have provided an of import constraint on bounding main 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 body of water interior reflects but the convolution of their atmospheric time evolution and body of water apportionment and mixing.

CFC and SF_six tracer-derived age of sea water [edit]

Chlorofluorocarbons (CFCs) are anthropogenic compounds that take 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 droplets cans, and as solvents.^[38] The entry of CFCs into the ocean makes them extremely useful as transient tracers to gauge rates and pathways of sea apportionment and mixing processes.^[39] However, due to production restrictions of CFCs in the 1980s, atmospheric concentrations of CFC-eleven and CFC-12 has stopped increasing, and the CFC-11 to CFC-12 ratio in the temper have been steadily decreasing, making h2o dating of water masses more problematic.^[39] Incidentally, production and release of sulfur hexafluoride (SF₆) have rapidly increased in the temper since the 1970s.^[39] Like to CFCs, SF₆ is also an inert gas and is not affected by oceanic chemical or biological activities.^[40] Thus, using CFCs in concert with SF₆ as a tracer resolves the water dating problems due to decreased CFC concentrations.

Using CFCs or SF₆ as a tracer of ocean apportionment 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 terminal in contact with the atmosphere is the tracer-derived age.^[41] Estimates of age can exist derived based on the partial force per unit area of an private chemical compound and the ratio of the partial pressure of CFCs to each other (or SF_six).^[41]

Fractional pressure and ratio dating techniques [edit]

The age of a water bundle tin be estimated by the CFC partial force per unit area (pCFC) age or SF_half-dozen partial pressure (pSF_half-dozen) age. The pCFC age of a water sample is defined every bit:

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

where [CFC] is the measured CFC concentration (pmol kg^−ane) and F is the solubility of CFC gas in seawater every bit a function of temperature and salinity.^[42] The CFC partial force per unit area is expressed in units of 10–12 atmospheres or parts-per-trillion (ppt).^[43] The solubility measurements of Chlorofluorocarbon-11 and CFC-12 accept been previously measured past Warner and Weiss^[43] Additionally, the solubility measurement of Cfc-113 was measured past Bu and Warner^[44] and SF₆ by Wanninkhof et al.^[45] and Bullister et al.^[46] Theses authors mentioned above have expressed the solubility (F) at a total pressure level of i atm as:

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

where F = solubility expressed in either mol l^−one or mol kg⁻¹ atm⁻¹, T = absolute temperature, S = salinity in parts per thousand (ppt), a₁, a₂, a_three, b_ane, b₂, and b₃ are constants to be determined from the least squares fit to the solubility measurements.^[44] This equation is derived from the integrated Van 't Hoff equation and the logarithmic Setchenow salinity dependence.^[44]

It can exist noted that the solubility of CFCs increase with decreasing temperature at approximately i% per degree Celsius.^[41]

One time the partial pressure of the CFC (or SF_{half dozen}) is derived, information technology is and so compared to the atmospheric fourth dimension histories for CFC-11, CFC-12, or SF₆ in which the pCFC straight corresponds to the yr with the aforementioned. The difference between the corresponding date and the collection date of the seawater sample is the average age for the water bundle.^[41] The age of a package of water tin also be calculated using the ratio of two CFC partial pressures or the ratio of the SF_{half dozen} partial force per unit area to a CFC partial force per unit area.^[41]

Rubber [edit]

According to their material safe data sheets, CFCs and HCFCs are colorless, volatile, non-toxic liquids and gases with a faintly sweet ethereal scent. Overexposure at concentrations of xi% or more may cause dizziness, loss of concentration, central nervous organization depression or cardiac arrhythmia. Vapors readapt air and can cause asphyxiation in bars spaces. Although non-flammable, their combustion products include hydrofluoric acid and related species.^[47] Normal occupational exposure is rated at 0.07% and does non pose any serious health risks.^[48]

References [edit]

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External links [edit]

• 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)
• Chlorofluorocarbon illegal trade
• History of halon-use by the US Navy Archived 2000-08-xix at the Wayback Auto
• Ozone Loss: The Chemic Culprits
• Process using pyrolysis in an ultra high temperature plasma arc, for the elimination of CFCs Archived 2016-04-15 at the Wayback Car
• [1] Ecology Investigation Agency: Reports etc. on illegal merchandise and solutions
• [2] Environmental Investigation Bureau in the USA: Reports etc. on illegal trade and solutions
• Freon in auto A/C
• [3] Phasing out halons in extinguishers

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Source: https://en.wikipedia.org/wiki/Chlorofluorocarbon

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