Figure dos reveals reconstruction of your percentages out-of CFC-11/CFC-several and you will CFC-113/CFC-several for the remote Us heavens. The fresh proportion off CFC-11/CFC-a dozen inside heavens enhanced substantially about later 1940s in order to throughout the 1977, and therefore regarding CFC-113/CFC-twelve got a moderate increase from inside the 1980s.
Relationships with other Atmospheric Smoke, 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.
As we are able to use Henry’s law to understand visible CFC years to have private CFC ingredients, there are even variations in the brand new percentages of atmospheric CFC concentrations which can be used to own relationship
The earliest reported measurement of the atmospheric concentration of SF6 was 0.03 pptv in 1970 (Lovelock, 1971). SF6 is accumulating rapidly in the atmosphere with a current growth rate of more than 7% per year. The historical atmospheric mixing ratio https://datingmentor.org/american-dating/ of SF6 has been reconstructed from production records and atmospheric measurements (Ko et al., 1993; Elkins et al., 1996; Maiss et al., 1996; Geller et al., 1997; Levin and Hesshaimer, 1996), and retrieved from concentrations measured in seawater (Law et al., 1994) and in previously-dated groundwater (Busenberg and Plummer, unpub. data). Figure 1 shows a preliminary reconstruction of northern hemisphere SF6 mixing ratios. As atmospheric CFC concentrations fall, an even more sensitive dating tool will be the ratio of SF6 to, for example, CFC-12 (Figure 2). However, because of the low solubility of SF6 (Mroczek, 1997), apparent ages can be very sensitive to excess air, so this needs to be accurately determined.
Busenberg and Plummer (1997) used SF6 successfully to date shallow groundwater on the Delmarva Peninsula, Maryland, and water from springs in the Blue Ridge Mountains of Virginia. Although SF6 is mostly of anthropogenic origin, concentrations between one and two orders of magnitude higher than that possible for modern air-water equilibrium were measured in groundwater from volcanic rift zones in New Mexico and Idaho (Busenberg and Plummer, 1997). There is likely a natural, igneous source of SF6 that will complicate dating in some environments. SF6 has also been used as an artificial tracer (Wilson and Mackay, 1996; Schlatter et al., 1997) that is injected into groundwater or surface water. Clark et al. (1995b) found that wastewater discharged to the Hudson River at New York City was contaminated with SF6. Busenberg and Plummer (1997) found minor contamination of SF6 in Rio Grande water near an outfall from a sewage treatment plant. All other surface waters had SF6 concentrations near equilibrium with air.
Of many techniques can be found during charge as well as in this new groundwater environment you to definitely can affect CFC density past those put by the sky-h2o harmony, and therefore apply at interpretation of noticeable years. Dining table dos directories the initial procedure, the affect noticeable CFC years, and you may cousin characteristics.
Contour step 3 Levels out of CFC-eleven, CFC-a dozen, and CFC-113 in the water recharged anywhere between 1940 and you can 1998 during the temperature of 5 so you can twenty-five °C in the sea-level.
magnitude old mistakes that come from uncertainties into the cost temperature. Particularly, when your CFC-eleven amount are 600 pg kg -1 in a certain h2o attempt you to definitely billed at 15°C, but cost heat try erroneously thought getting 5°C, a noticeable ages which is particular 12 years too-old would become tasked, based on CFC-11. A suspicion into the cost heat regarding ± 2°C results in decades uncertainties out-of three years otherwise reduced to own water charged in advance of regarding 1990 (Busenberg mais aussi al., 1993). Over-quote of charge heat results in apparent many years too young, and you can not as much as-estimation gives ages which might be biased dated. Uncertainty for the demand temperature of ± 2°C contributes to uncertainty from inside the apparent CFC period of one year otherwise reduced having h2o energized prior to the mid-1970s. Although not, as heavens collection ratios peaked regarding the middle- and you may late-90s, CFC visible ages turned extremely sensitive to concerns during the cost temperatures.