This document is also available in format: fs Information about the age of ground water can be used to define recharge rates, refine hydrologic models of ground-water systems, predict contamination potential, and estimate the time needed to flush contaminants from ground-water systems. CFCs also can be used to trace seepage from rivers into ground-water systems, provide diagnostic tools for detection and early warning of leakage from landfills and septic tanks, and to assess susceptibility of water-supply wells to contamination from near-surface sources. During the past 50 years, human activities have released an array of chemical and isotopic substances to the atmosphere. In the atmosphere, these substances have mixed and spread worldwide. Young ground water is typically found at depths from 0 to feet in unconsolidated sediments and at depths up to feet in fractured-rock systems.
Chlorofluorocarbons are stable, synthetic organic compounds that were developed in the early s as safe alternatives to ammonia and sulfur dioxide in refrigeration and have been used in a wide range of industrial and refrigerant applications.
CFC and CFC were used as coolants in air conditioning and refrigeration, blowing agents in foams, insulation, and packing materials, propellants in aerosol cans, and as solvents.
CFC has been used primarily by the electronics industry in semiconductor chip manufacturing, in vapor degreasing and cold immersion cleaning of microelectronic components, and surface cleaning. Probably better known to the public as Freon TMCFCs are nontoxic, nonflammable and noncarcinogenic, but they contribute to ozone depletion.
This agreement, the Montreal Protocol on Substances That Deplete the Ozone Layer, was strengthened in and again in when was established as the cut-off date for CFC production in industrialized countries.
Tritium half-life Although it is difficult to evaluate age information from tritium data alone, age commonly can be reliably determined from data on tritium 3 H and its decay product, helium-3 3 He. Several conditions are necessary to solve the calculation and interpret the age: 1 The sample must contain detectable 3 H greater than approximately 0.
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Krypton 85 Kr has also been used to date ground water. The source for atmospheric input of 85 Kr is reprocessing of fuel rods from nuclear reactors. Because of difficulties in collection and analysis, 85 Kr is not yet a practical dating tool for ground-water studies. CFCs and nitrate concentrations were measured between June and January on a section of the Delmarva Peninsula, in the Fairmount watershed. Ground-water dating reveals a pattern of high nitrate concentrations moving slowly toward the estuary.
Alternatives to using CFCs in dating ground water will clearly be needed as atmospheric CFC concentrations continue to fall.
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Industrial production of SF 6 began in with the introduction of gas-filled high-voltage electrical switches. SF 6 is extremely stable and is accumulating rapidly in the atmosphere. The historical atmospheric mixing ratio of SF 6 is being reconstructed from production records, archived air samples, and atmospheric measurements, and retrieved from concentrations measured in seawater and in previously-dated ground water.
A preliminary reconstruction has been made of northern-hemisphere SF 6 mixing ratios figure far left. Although SF 6 is almost entirely of human origin, there is likely a natural, igneous source of SF 6 that will complicate dating in some environments. Additional comments and case studies. For best results, the apparent age should be determined using multiple dating techniques because each dating technique has limitations.
CFC dating is best suited for ground water in relatively rural environments where localized contamination, such as that from septic systems, sewage effluent, landfills, or urban runoff, can contain CFC concentrations in excess of that of atmospheric sources.
Even where there are problems with CFC dating of ground water, the presence of CFCs indicates that the water sample contains at least some posts water, making CFCs useful as tracers of recent recharge. Delmarva Peninsula Results from the determination of CFCs in some agricultural areas on the Delmarva Peninsula of Maryland and Virginia indicate that water recharged since the early s exceeds the U. Nitrate concentrations in ground water under woodlands were low, whereas ground water recharged under agricultural fields had nitrate concentrations that exceeded the MCL.
Thus, even if the application of nitrogen fertilizers to the fields stopped today, streams, rivers, and estuaries can be expected to receive increasing amounts of nitrate from ground-water discharge until the contaminated water is flushed through the system Modica and others, ; up to 30 years may be needed to flush the high-nitrate water present in several small agricultural watersheds.
Central Oklahoma Water discharged from deep to feet municipal supply wells in the central Oklahoma aquifer contains CFCs Busenberg and Plummer, This unexpected finding indicated that shallow ground water was being mixed with deep, older water during pumping.
In this case, CFCs were a valuable tracer for testing hydraulic seals of municipal water wells and their susceptibility to contamination. By measuring CFC concentrations in groundwater and determining or estimating the recharge temperature of the groundwater, a CFC-model age can be assigned to the sample. Apparent CFC ages are obtained by converting measured CFC concentrations in groundwater to equivalent air concentrations using known solubility relationships Warner and Weiss, ; Bu and Warner, and the recharge temperature.
Corrections for excess air are made if appropriate Busenberg and Plummer, These concentrations are compared with the atmospheric concentration curve to obtain an apparent CFC age. The sensitivity of the CFC dating method depends on the rate of change of the atmospheric CFC concentration with time, and thus the ability to date very young water will diminish with time. However, the ability to date groundwater that entered the saturated zone prior to the Year will not change for several decades.
This corresponds to an error in apparent CFC ages of less than 1 year for groundwaters recharged since the mid s Dunkle et al.
The sensitivity of apparent CFC age to excess air is less than 0. One of the assumptions of groundwater dating with CFCs is that concentrations in the soil gas immediately above the water table are in equilibrium with the atmosphere. However, this is not always the case, particularly if the unsaturated zone is thick Weeks et al.
A time lag associated with gas diffusion through the unsaturated zone is strongly dependent on the soil water content and CFC solubility, and to a lesser extent on the recharge rate. This time lag is negligible if the unsaturated zone thickness is less than 5 m, and varies between 0.
The effect of dispersion on apparent CFC concentrations and ages has been discussed by Busenberg and PlummerPlummer et al. Because the atmospheric concentration curve is approximately linear with time, dispersion has a minimal effect on concentration profiles. Modeling results show that only waters older than 20 years are significantly affected. For dispersivities of less than 0.
Sorption of CFCs to aquifer materials may cause CFC velocities to be lower than water velocities in some aquifers, resulting in apparent CFC ages which are older than groundwater ages Cook et al. However, sorption of CFCs does not appear to be important processes in low organic carbon aquifers. Contamination of groundwater with chlorofluorocarbons appears to be the greatest limitation to CFC dating.
Other organic contaminants may contain small quantities of CFCs, sufficient to cause serious contamination at the parts per trillion level. Groundwater samples from residential and industrial sites often contain concentrations of chlorofluorocarbons above modern atmospheric levels, in some instances by several orders of magnitude Thompson and Hayes, ; Jackson et al. Elevated atmospheric concentrations may occur close to industrial centers Lovelock, ; Cook et al.
Source of text : This review was assembled by Eric Caldwell, primarily from Solomon et al.
Resources on Isotopes Periodic Table-Chlorofluorocarbons Chloroflourocarbons CFCs are anthropogenic organic compounds that have been produced since the s for a number of industrial and domestic purposes ranging from aerosol propellants to refrigerants. Bu, X. Solubility of chlorofluorocarbon in water and seawater. Deep Sea Res.
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Bullister, J. Busenberg, E. 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. Inthere were an estimated 5, kilotons of CFCs in existing products such as refrigerators, air conditioners, aerosol cans and others.
In 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. Patent was set to expire in In conjunction with other industrial peers DuPont formed a lobbying group, the "Alliance for Responsible CFC Policy," to combat regulations of ozone-depleting compounds.
The sensitivity of the CFC dating method depends on the rate of change of the atmospheric CFC concentration with time, and thus the ability to date very young water will diminish with time. However, the ability to date groundwater that entered the saturated zone prior to the Year will not change for several decades. The Reston Groundwater Dating Laboratory provides analytical services for chlorofluorocarbons (CFCs), sulfur hexafluoride (SF 6) and other dissolved gases including N 2, Ar, CO 2, CH 4, O 2. The lab also administers the USGS contract for tritium/helium-3 .
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 and by the volatile organic compounds VOC directive of the EU in 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 Januarybased on the Montreal Protocol and guidelines of the European Union. Production of new stocks ceased in most probably all countries in There are also a few other, highly specialized uses. These programs recycle halon through "halon banks" coordinated by the Halon Recycling Corporation  to ensure that discharge to the atmosphere occurs only in a genuine emergency and to conserve remaining stocks.
These included Suva refrigerants and Dymel propellants.
Hydrofluorocarbons are included in the Kyoto Protocol because of their very high Global Warming Potential and are facing calls to be regulated under the Montreal Protocol [ dubious - discuss ]  due to the recognition of halocarbon contributions to climate change.
On 21 Septemberapproximately countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely by in a United Nations -sponsored Montreal summit.
Developing nations were given until Many nations, such as the United States and Chinawho had previously resisted such effortsagreed with the accelerated phase out schedule.
Work on alternatives for chlorofluorocarbons in refrigerants began in the late s 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. Among the natural refrigerants along with ammonia and carbon dioxidehydrocarbons 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.
In Metered-dose inhalers MDIa non-ozone effecting substitute was developed as a propellant, known as " hydrofluoroalkane.
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.
Chlorofluorocarbons CFCs are anthropogenic compounds that have been released into the atmosphere since the s in various applications such as in air-conditioning, refrigeration, blowing agents in foams, insulations and packing materials, propellants in aerosol cans, and as solvents.
Using CFCs or SF 6 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. The pCFC age of a water sample is defined as:.
The difference between the corresponding date and the collection date of the seawater sample is the average age for the water parcel. According to their material safety data sheets, CFCs and HCFCs are colorless, volatile, non-toxic liquids and gases with a faintly sweet ethereal odor.
Vapors displace air and can cause asphyxiation in confined spaces.
The CFC Singles would like to resume meeting for lunch and fellowship on Sundays. So beginning June 28, at around noon anyone who wants to join us can bring their lunch and a chair and meet us at Van Park where we will eat while socially distancing. The party is shady with plenty of room. It does not have restroom facilities, however. CFC dating is best suited for ground water in relatively rural environments where localized contamination, such as that from septic systems, sewage effluent, landfills, or urban runoff, can contain CFC concentrations in excess of that of atmospheric sources. The sensitivity of the CFC dating method depends on the rate of change of the atmospheric CFC concentration with time, and thus the ability to date very young water will diminish with time. However, the ability to date groundwater that entered the saturated zone before the year will not change for several decades.
Although non-flammable, their combustion products include hydrofluoric acid, and related species. From Wikipedia, the free encyclopedia. For other singular uses, see CFC disambiguation.
Main article: Organofluorine chemistry. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed.
February Learn how and when to remove this template message. Bibcode : HWM Chris; Bernath, P.
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Journal of Quantitative Spectroscopy and Radiative Transfer. Archived from the original on New Series. Bibcode : Sci Feng Atmospheric Environment.
Bibcode : AtmEn. Dispose of old CFCs". Retrieved Scientific American Inventions and Discoveriesp. March United Nations Environmental Programme.
Korea to ban import, production of freon, halon gases in Archived at the Wayback Machine. Yonhap News Agency. Retrieved on 24 September