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Processes that may Modify Noticeable CFC Decades

Processes that may Modify Noticeable CFC Decades

Profile dos suggests repair of your ratios out-of CFC-11/CFC-a dozen and CFC-113/CFC-a dozen in the secluded Us sky. The fresh new ratio regarding CFC-11/CFC-twelve inside the heavens increased significantly regarding late 1940s so you can on 1977, hence off CFC-113/CFC-twelve got a moderate increase in the 1980s.

Relationship along with other Atmospheric Gases, 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 legislation so you can interpret apparent CFC many years getting individual CFC substances, there are even variations in the new rates away from atmospheric CFC levels which can be used getting matchmaking

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 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 are present through the charge along with the newest groundwater ecosystem one to can impact CFC concentrations past men and women put by air-liquid harmony, and therefore connect with interpretation off visible many years. Desk dos listings the most important process, its impact on apparent CFC decades, and you may relative pros.

Profile step 3 Concentrations off CFC-11, CFC-12, and CFC-113 within the water charged between 1940 and you can 1998 in the temperature regarding 5 to help you 25 °C from the sea level.

magnitude adventist singles connection com of age errors you to definitely come from concerns into the cost temperatures. Like, should your CFC-eleven attention is actually 600 pg kilogram -1 in a certain drinking water decide to try you to energized within 15°C, but recharge temperature was erroneously believed become 5°C, an apparent ages that is particular a dozen many years too-old perform end up being tasked, according to CFC-eleven. A suspicion in the cost temperatures off ± 2°C causes age concerns out-of three years otherwise quicker to possess liquid charged just before on 1990 (Busenberg ainsi que al., 1993). Over-estimate of cost temperature leads to noticeable ages too young, and you can less than-quote gives many years which can be biased old. Uncertainty during the charge temperatures from ± 2°C results in suspicion during the visible CFC period of 1 year otherwise shorter getting drinking water charged before the mid-seventies. not, once the air collection rates peaked on middle- and you may late-90s, CFC visible age turned into very responsive to concerns inside the charge temperature.

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