HR: 1340h
AN: OS13B-0530    [Abstracts]
TI: Trifluoromethyl Sulfur Pentafloride (SF5CF3), a Gas With Potential for Tracer Release Experiments
AU: * Smethie, W M
EM: bsmeth@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, P.O. Box 1000, Palisades, NY 10964 United States
AU: Ledwell, J R
EM: jledwell@whoi.edu
AF: Woods Hole Oceanographic Institution, Mail Stop 12, Woods Hole, MA 02543 United States
AU: Ho, D T
EM: david@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, P.O. Box 1000, Palisades, NY 10964 United States
AB: SF5CF3 is chemically similar to SF6, a gas which has been used extensively in tracer release experiments, with a CF3 group substituted for a F atom in the molecular structure. It is a gas at atmospheric pressure and is present in the atmosphere with a mixing ratio of 0.12 ppt in 1999 [Sturges et al., Science, 289, 2000]. Sturges et al. (2000) measured a vertical profile of SF5CF3 and SF6 in Antarctic firn ice, showing that it has existed in the atmosphere for the last 3 decades and has increased over time with a trend that nearly parallels the increase of SF6. This suggests that its source could be related to the production and use of SF6, but there are also industrial processes for which it is a by-product. However, the exact source is not understood at this time. SF5CF3 is chemically stable with an estimated atmospheric lifetime of about 800 years [Takahashi et al., Geophys. Res. Lett., 29, 2002]. Because of its very low mixing ratio in the atmosphere and its chemical stability, it has very high potential for use in tracer release experiments. We have carried out some preliminary experiments to evaluate this potential. SF5CF3 can be measured in water samples by the same purge and trap - gas chromatographic procedure used for CFCs, has an ECD sensitivity slightly greater than SF6, and has a linear ECD response up to at least 80 fmoles. A preliminary determination of its solubility in fresh water revealed an Ostwald coefficient of 0.031 at 25 deg C, which is about half that of SF6. Its Ostwald coefficient in 1-octonol was measured to be about 3, roughly 7 times greater than for SF6. This suggests that SF5CF3 will have a greater affinity for organic matter than SF6. In open ocean tracer release experiments, SF6 is slowly transported downward in addition to its vertical spreading by diapycnal mixing. This could be caused by adsorption and release from sinking particles with organic phases, but the solubility of SF6 and SF5CF3 in 1-octanol indicate this effect is too small to account for the transport. We will continue our investigation of the suitability of using SF5CF3 in ocean tracer release experiments by better determining its solubility, determining partition coefficients between seawater and various types of particulate matter, and performing a tracer release experiment in the Santa Monica Basin along with SF6 to directly compare the behavior of these two trace gases.
DE: 4808 Chemical tracers
DE: 4820 Gases
DE: 4294 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting