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Chlorofluorocarbons(CFCs) are stable, synthetic, halogenated alkanes, developed in the early 1930s as safe alternatives to ammonia and sulphur dioxide in refrigeration. Production and release - World production and release of CCl (Fluorocarbons 11 and 12) through 1975. Production of CFC-12 (dichlorodifluoromethane, CF2Cl2) began in 1931 followed by CFC-11 (trichlorofluoromethane) in 1936.
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This indicated the potential for use of CFCs as tracers in porous media where moderately adsorbing tracers could not be used. (1976) demonstrated the use of CFC-11 in tracing groundwater recharge of sewage effluent discharged to dry washes and riverbeds near Tucson, Arizona.
Randall and Schultz (1976) introduced a method to date a water sample with CFC-11 in relation to an analysis of another water sample of known age, and to determine age from analysis of a single water sample through Henry's law solubility.
Many other CFC compounds have since been produced, most notably CFC-113 (trichlorotrifluoroethane, C2F3Cl3).
CFCs are nonflammable, noncorrosive, nonexplosive, very low in toxicity, and have physical properties conducive to a wide range of industrial and refrigerant applications.
Methods of collection and preservation of water samples prior to analysis have also evolved. (1992) Consumption of Freon CFC-11 and CFC-12 by anaerobic sediments and soils.
In the first groundwater studies (1970s), CFC analyses were performed in the field immediately after collection in glass syringes. The sample collection procedure is conducted under water in a beaker to isolate the atmosphere from the water sample in the bottle. (1995) OAXTC 92: Ocean/Atmosphere Exchange of Trace Compounds 1992: Oceanic measurements of HCFC-22, CFC-11, CFC-12, CFC-113, CHO in the marine air and surface waters of the west Pacific Ocean (August 3-October 21, 1992). In the following, we discuss the interpretation of temporal aspects of CFC concentrations measured in air, soil air, and groundwater. The feasibility of using CFCs as tracers of recent recharge and indicators of groundwater age was first recognized in the 1970s (Thompson et al., 1974; Schultz et al., 1976; Randall and Schultz, 1976; Thompson, 1976; Hayes and Thompson, 1977; Randall et al., 1977; Thompson and Hayes, 1979; Schultz, 1979). (1974) conducted tracer tests by injecting fluorescein dye, and later a solution containing 100 mg kg-1 of CFC-11 into an aquifer of poorly sorted sand and gravel. The fluorescein dye was not recovered whereas the CFC-11 arrived at a nearby monitoring well within the expected travel time. By measuring concentrations of CFC-12, CFC-11 and CFC-113, it is possible to identify groundwater recharged since approximately 1941, 1947, and 1955, respectively.Tags: Adult Dating, affair dating, sex dating