Profile dos shows repair of one’s ratios from CFC-11/CFC-12 and CFC-113/CFC-twelve during the secluded North american air. The latest ratio out of CFC-11/CFC-twelve within the sky improved substantially from the late 1940s to regarding 1977, and that out-of CFC-113/CFC-12 had a moderate increase when you look at the eighties.
Relationships along with other Atmospheric Fumes, Sulfurhexafluoride
The slowing and turnover of CFC atmospheric mixing ratios in the 1990s has resulted in ambiguity in CFC-based apparent age. Sulphur hexafluoride (SFsix) has been developed as an alternative to CFCs for gas-solubility dating of water (Busenberg and Plummer, 1997). Significant production of SF6 began in the 1960s for use in high voltage electrical switches. SF6 is extremely stable, with an estimated atmospheric lifetime of 800 (Morris et al., 1995) to 3200 years (Ravishankara et al., 1993). SF6 can be analysed by GC-ECD techniques to a precision of 1-3% (Wanninkhof et al., 1991; Law et al., 1994), so, even though atmospheric mixing ratios are small (currently about 10 pptv), dating is possible from about 1970 to the present.
While we may use Henry’s law so you can interpret obvious CFC ages getting individual CFC compounds, there are even variations in the brand new percentages out of atmospheric CFC density which can be used to possess matchmaking
The earliest reported measurement of the atmospheric concentration of SF6 was 0.03 pptv in 1970 (Lovelock, 1971). (suite…)