Primary uses of CFC-11 and CFC-12 include refrigerants in air-conditioning and other coolers, blowing agents in foams, insulation, and packing materials, propellants in aerosol cans, and as solvents.
CFC-113 has been used primarily by the electronics industry in manufacture of semiconductor chips, in vapour degreasing and cold immersion cleaning of microelectronic components, and as a solvent in surface cleaning procedures (Jackson et al., 1992).
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.
Groundwater dating with CFC-11, CFC-12 and CFC-113 is possible because (1) the atmospheric mixing ratios of these compounds are known and/or have been reconstructed from 1940 to the present, (2) the Henry's law solubilities in water are known, and (3) concentrations in air and young water are relatively high and can be measured. (1996) Sulfur hexafluoride - A powerful new atmospheric tracer.
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.
CFCs used in refrigeration and airconditioning have somewhat greater storage times, being released on average within 10 years, and CFCs used as blowing agents in closed-cell thermoset foams are released after more than 10 years (Midgley and Fisher, 1993). (1992) Effects of atmospheric pressures on gas transport in the vadose zone.
Current estimates of the atmospheric lifetimes of CFC-11, CFC-12, and CFC-113 are 45 7, 87 17, and 100 32 years (Volk et al., 1997).
CFCs provide excellent tracers and dating tools of young water (1940 to present time scale). CFC-11, CFC-12 and CFC-113 concentrations in water can be determined to a detection limit of about 0.3 picograms per kg of water (pg/kg-1) using purge and trap, gas chromatographic techniques with electron-capture detector (GC-ECD; Bullister, 1984; Bullister and Weiss, 1988; Busenberg and Plummer, 1992). 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. 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.