Chlorofluorocarbon
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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
Structure, properties and production
As in simpler
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.
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 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 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.[8]
Another equation that can be applied to get the correct molecular formula of the CFC/R/Freon class compounds is 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.[9]
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, R-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 reaction of the CFCs which is responsible for the depletion of ozone, is the
- 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.[11]
Impact as greenhouse gases
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 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
The strength of CFC absorption bands and the unique susceptibility of the atmosphere at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb radiation
Groups are actively disposing of legacy CFCs to reduce their impact on the atmosphere.[20]
According to NASA in 2018, the hole in the ozone layer has begun to recover as a result of CFC bans.[21] However, research released in 2019 reports an alarming increase in CFCs, pointing to unregulated use in China.[22]
History
Prior to, and during the 1920s, refrigerators used toxic gases as refrigerants, including ammonia, sulphur dioxide, and chloromethane. Later in the 1920s after a series of fatal accidents involving the leaking of chloromethane from refrigerators, a major collaborative effort began between American corporations Frigidaire, General Motors, and DuPont to develop a safer, non-toxic alternative. Thomas Midgley Jr. of General Motors is credited for synthesizing the first chlorofluorocarbons. The Frigidaire corporation was issued the first patent, number 1,886,339, for the formula for CFCs on December 31, 1928. 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[23] in 1930.[24][25]
By 1930, General Motors and Du Pont formed the Kinetic Chemical Company to produce Freon, and by 1935, over 8 million refrigerators utilizing R-12 were sold by Frigidaire and its competitors. In 1932, Carrier began using R-11 in the worlds first self-contained home air conditioning unit known as the "atmospheric cabinet". As a result of CFCs being largely non-toxic, they quickly became the coolant of choice in large air-conditioning systems. Public health codes in cities were revised to designate chlorofluorocarbons as the only gases that could be used as refrigerants in public buildings.[26]
Growth in CFCs continued over the following decades leading to peak annual sales of over 1 billion USD with greater than 1 million metric tonnes being produced annually. It wasn't until 1974 that it was first discovered by two University of California chemists, Professor F. Sherwood Rowland and Dr. Mario Molina, that the use of chlorofluorocarbons were causing a significant depletion in atmospheric ozone concentrations. This initiated the environmental effort which eventually resulted in the enactment of the Montreal Protocol.[27][28]
Commercial development and use in fire extinguishing
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 under the same restrictions, instead, the consumption of bromofluoroalkanes was frozen at 1986 levels. This is due to the fact that emergency discharge of extinguishing systems was thought to be too small in volume to produce a significant impact, and too important to human safety for restriction.[29]
Regulation
Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the
By 1987, in response to a dramatic seasonal depletion of the ozone layer over
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
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.[36][37][38]
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.[39] Approximately one-third of these CFCs are projected to be emitted over the next decade[when?] if action is not taken, posing a threat to both the ozone layer and the climate.[40] A proportion of these CFCs can be safely captured and destroyed by means of high temperature, controlled incineration which destroys the CFC molecule.[41]
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.[42] In 1986 DuPont, with new patents in hand, reversed its previous stance and publicly condemned CFCs.[43] 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.[43]
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
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.[44][45][46] 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[47] 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.
Phasing-out of HFCs and HCFCs
Hydrofluorocarbons are included in the
On September 21, 2007, approximately 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely by 2020 in a
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 have been said to pose an immediate threat to our environment.[55] 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.[56]
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
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.[58] Various other solvents and methods have replaced the use of CFCs in laboratory analytics.[59]
In Metered-dose inhalers (MDI), a non-ozone effecting substitute was developed as a propellant, known as "hydrofluoroalkane."[60]
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) | HCFC-225cb (C3HCl2F5) |
Development of Hydrofluoroolefins as alternatives to CFCs and HCFCs
The development of Hydrofluoroolefins (HFOs) as replacements for Hydrochlorofluorocarbons and Hydrofluorocarbons began after the Kigali amendment to the Montreal Protocol in 2016, which called for the phase out of high global warming potential (GWP) refrigerants and to replace them with other refrigerants with a lower GWP, closer to that of carbon dioxide.[61] HFOs have an ozone depletion potential of 0.0, compared to the 1.0 of principal CFC-11, and a low GWP which make them environmentally safer alternatives to CFCs, HCFCs and HFCs.[62][63]
Hydrofluoroolefins serve as functional replacements for applications where high GWP hydrofluorocarbons were once used. In April 2022, the EPA signed a pre-published final rule Listing of HFO-1234yf under the Significant New Alternatives Policy (SNAP) Program for Motor Vehicle Air Conditioning in Nonroad Vehicles and Servicing Fittings for Small Refrigerant Cans. This ruling allows HFO-1234yf to take over in applications where ozone depleting CFCs such as R-12, and high GWP HFCs such as R-134a were once used.[64] The phaseout and replacement of CFCs and HFCs in the automotive industry will ultimately reduce the release of these gases to atmosphere and intern have a positive contribution to the mitigation of climate change.[65][66]
Tracer of ocean circulation
Since 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.[67] 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.[68] 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.[68] Incidentally, production and release of sulfur hexafluoride (SF6) have rapidly increased in the atmosphere since the 1970s.[68] Similar to CFCs, SF6 is also an inert gas and is not affected by oceanic chemical or biological activities.[69] 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.[70] 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).[70]
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.[71] The CFC partial pressure is expressed in units of 10–12 atmospheres or parts-per-trillion (ppt).[72] The solubility measurements of CFC-11 and CFC-12 have been previously measured by Warner and Weiss[72] Additionally, the solubility measurement of CFC-113 was measured by Bu and Warner[73] and SF6 by Wanninkhof et al.[74] and Bullister et al.[75] 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.[73] This equation is derived from the integrated Van 't Hoff equation and the logarithmic Setchenow salinity dependence.[73]
It can be noted that the solubility of CFCs increase with decreasing temperature at approximately 1% per degree Celsius.[70]
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.[70] 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.[70]
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
References
- ^ "Climate Change". The White House. 19 March 2021. Archived from the original on 19 March 2021. Retrieved 11 April 2022.
- .
- ^ Darby, Megan (19 August 2014). "Ozone layer treaty could tackle super polluting HFCs". rtcc.org. Archived from the original on 19 August 2014. Retrieved 11 April 2022.
- ^ "Hydrofluoroolefins". GAB Neumann GmbH. Retrieved 2023-12-12.
- ISBN 978-1-4613-7057-4.
- ^ "Ice Breaker: Refrigerant Numbering System Explained | ACHR News". www.achrnews.com. Retrieved 2023-12-12.
- ^ Sievänen, Esa (2020-02-26). "Numbering of refrigerants • Darment". Darment. Retrieved 2023-12-12.
- ^ "NOAA Global Monitoring Laboratory - Halocarbons and other Atmospheric Trace Species". gml.noaa.gov. Retrieved 2023-12-12.
- ^ "Halons Program". 15 July 2015.
- ^ "The NOAA Annual Greenhouse Gas Index (AGGI)". NOAA.gov. National Oceanographic and Atmospheric Administration (NOAA). Spring 2023. Archived from the original on 24 May 2023.
- ^ "Appendix 8.A" (PDF). Intergovernmental Panel on Climate Change Fifth Assessment Report. p. 731. Archived (PDF) from the original on 2017-10-13. Retrieved 2020-07-15.
- (PDF) from the original on 2015-04-03.
- S2CID 33736550.
- ^ 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
- ^ .
- ISBN 1107021553
- ^ 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
- ^ "One overlooked way to fight climate change? Dispose of old CFCs". Environment. 2019-04-29. Archived from the original on 2019-04-29. Retrieved 2019-04-30.
- ^ Samson Reiny (4 January 2018). "NASA Study: First Direct Proof of Ozone Hole Recovery Due to Chemicals Ban". NASA. Archived from the original on 24 September 2020. Retrieved 2 October 2019.
- ^ CFC use in China
- ^ Bellis, Mary (12 August 2016). "Where Does Freon Come From?". ThoughtCo. Retrieved 11 April 2022.
- OCLC 53284995.
- ISBN 978-0-393-32183-8. Retrieved 11 April 2022. (as reviewed in the Journal of Political Ecology Archived 2004-03-28 at the Wayback Machine)
- ^ "NOAA Global Monitoring Laboratory - Halocarbons and other Atmospheric Trace Species". gml.noaa.gov. Retrieved 2023-12-12.
- ^ "Chlorofluorocarbons and Ozone Depletion". American Chemical Society. Retrieved 2023-12-12.
- ^ "Back from the brink: how the world rapidly sealed a deal to save the ozone layer". rapidtransition.org. Retrieved 2023-12-12.
- ^ "Vienna Convention for the Protection of the Ozone Layer". legal.un.org. Retrieved 2023-12-12.
- .
- ^ Auer, Charles, Frank Kover, James Aidala, Marks Greenwood. "Toxic Substances: A Half Century of Progress". Archived 2021-07-02 at the Wayback Machine. EPA Alumni Association. March 2016.
- United Nations Environmental Programme. 2007. Web. 3 April 2011.
- ^ S. Korea to ban import, production of freon, halon gases in 2010. Archived 2014-08-10 at the Wayback Machine. Yonhap News Agency. 23 December 2009
- ^ "Ozonkiller: Ein verbotener Stoff in der Atmosphäre – WELT". Welt.de (in German). 16 May 2018. Archived from the original on 2020-10-05. Retrieved 2018-05-18.
- ^ "Ozone hole-forming chemical emissions increasing and mysterious source in East Asia may be responsible". Independent.co.uk. 16 May 2018. Archived from the original on 2020-11-09. Retrieved 2018-05-18.
- ^ https://www.dcceew.gov.au/environment/protection/ozone/halon/essential-use-exeptions [bare URL]
- ^ "| Ozone Secretariat". ozone.unep.org. Retrieved 2023-12-12.
- ^ "Phase out of Halons : Firesafe.org.uk". www.firesafe.org.uk. Retrieved 2023-12-12.
- ^ Campbell, Nick et al. "HFCs and PFCs: Current and Future Supply, Demand and Emissions, plus Emissions of CFCs, HCFCs and Halons", Ch. 11 in IPCC/TEAP Special Report: Safeguarding the Ozone Layer and the Global Climate System
- ^ Chlorofluorocarbons: An Overlooked Climate Threat, EESI Congressional Briefing. Archived 2009-12-04 at the Wayback Machine. Eesi.org. Retrieved on 24 September 2011.
- ^ "The cool way to destroy CFCs". New Scientist. Retrieved 2023-12-12.
- ^ Desombre, E.R., 2000: Domestic Sources of International Environmental Policy: Industry, Environmentalists, and U.S. Power. MIT Press. SBN: 9780262041799. p. 93.
- ^ a b "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)
- ^ "Phaseout of Class I Ozone-Depleting Substances". 22 July 2015.
- ^ "Ozone depleting substances". Ministry for the Environment. 2021-04-01. Retrieved 2023-12-12.
- ^ https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1144969/20230320_JSP_418_Leaflet_7.pdf [bare URL PDF]
- ^ Welcome to the Halon Corporation. Archived 2009-09-19 at the Wayback Machine. Halon.org. Retrieved on 24 September 2011.
- ^ ISSN 2156-2202.
- ^ "Ozone Layer Depletion", U.S. Environmental Protection Agency. Archived 2008-09-19 at the Wayback Machine accessed 25 June 2008
- ^ Freon® : 1930. In Depth. Archived 2011-03-19 at the Wayback Machine. dupont.com (30 January 2009). Retrieved on 2011-09-24.
- ^ Broder, John M. (9 November 2010). "A Novel Tactic in Climate Fight Gains Some Traction". The New York Times. p. A9. Archived from the original on 20 May 2013. Retrieved 5 February 2013.
- PMID 17360370.
- ^ HCFC Phaseout Schedule. Archived 2009-07-16 at the Wayback Machine. Epa.gov (28 June 2006). Retrieved on 2011-09-24.
- ^ "India achieves complete phase out of one the most potent ozone depleting chemical". pib.gov.in. Retrieved 2022-06-02.
- ^ "Emissions of several ozone-depleting chemicals are larger than expected". MIT News | Massachusetts Institute of Technology. 17 March 2020. Retrieved 2022-10-18.
- ^ "Refrigerant Management @ProjectDrawdown #ClimateSolutions". Project Drawdown. 2020-02-06. Retrieved 2022-10-18.
- ^ acp.copernicus.org article (PDF)
- ^ "Greenpeace, Cool Technologies". Archived 2008-07-06 at the Wayback Machine. (PDF). Retrieved on 24 September 2011.
- ^ Use of Ozone Depleting Substances in Laboratories. TemaNord 516/2003 Archived February 27, 2008, at the Wayback Machine. Norden.org (1 January 2003). Retrieved on 2011-09-24.
- PMID 10743983.
- S2CID 53745498.
- ^ "The Environmental Benefits of HFOs". sustainability.honeywell.com. Retrieved 2023-12-12.
- ^ Dey, Anup Kumar (2023-07-11). "What are HFO Refrigerants? Their Benefits and Applications". What is Piping. Retrieved 2023-12-12.
- ^ https://www.aem.org/news/u-s-epa-prepublished-final-rule-approves-use-of-hfo1234yf-in-offroad-equipment [bare URL]
- ^ "Automobile Air Conditioners and Chlorofluorocarbons (CFCs)". p2infohouse.org. Retrieved 2023-12-12.
- ^ "Phasing Down HFCs". www.nrdc.org. 2022-08-09. Retrieved 2023-12-12.
- ^ 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 Archived 2016-04-15 at the Wayback Machine: Vienna, International Atomic Energy Agency.
- ^ from the original on 2020-07-28. Retrieved 2020-04-30.
- from the original on 2021-11-22. Retrieved 2017-11-03.
- ^ PMID 21329203. Archived from the original(PDF) on 2015-02-10. Retrieved 2015-01-31.
- .
- ^ .
- ^ .
- .
- from the original on 2015-09-24.
- ^ "Chlorofluorocarbon – an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-12-12.
- ^ Material Safety Data Sheet Archived 2011-02-08 at the Wayback Machine. National Refrigerants
- ^ WHO. "Fully Halogenated Chlorofluorocarbons". International Programme on Chemical Safety. Archived from the original on 2012-05-05.
External links
- Gas conversion table
- Nomenclature FAQ
- Class I Ozone-Depleting Substances
- Class II Ozone-Depleting Substances (HCFCs)
- History of halon-use by the US Navy Archived 2000-08-19 at the Wayback Machine
- Process using pyrolysis in an ultra high temperature plasma arc, for the elimination of CFCs Archived 2016-04-15 at the Wayback Machine
- Freon in car A/C
- Phasing out halons in extinguishers