Chlorofluorocarbons

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Chlorofluorocarbons (CFCs) are stable, synthetic, halogenated alkanes, developed in the early 1930’s as safe alternatives to ammonia and sulphur dioxide in refrigeration.

Water dating with CFC-11 CFC-12 and CFC-113 is possible because:

i. the atmospheric mixing ratios of these compounds are known and/or have been reconstructed over the past 50 years
ii. the Henry’s law solubilities in water are known, and
iii. concentrations in air and young water are relatively high and can be measured.

Waters carry small amounts of the gases in solution, the amount depending on the atmospheric concentrations at the time of recharge. So water samples are labelled by their CFC concentrations, from which the age of the water can be determined.

The method is best used with young waters (post-1970) and is complementary to our tritium dating facility which is better for dating older (pre-1970) waters.

Download: Sampling_Instructions_CFC.pdf (452.04 kB)