- Molecular Formula: CF3SF5
- Molar Mass: 196.055 g/mol
- Appearance: Colorless, odorless gas
- Boiling Point: -20 C
Use as a Tracer:
Transient tracers are chemicals with easily measurable concentrations that are used to explore ocean mixing. Controlled amounts of transient tracers are introduced into the atmosphere and then enter the ocean through injection or air-sea exchange. By measuring the concentration of the tracer over time, we can better-understand ocean mixing patterns.
Studies involving SF6 have provided insight to many different areas of Oceanography. SF6 is one of the most widely used tracers today; which can potentially cause interference between different experiments utilizing SF6. Today, there is a pressing need for an alternate tracer that can be used for large scale experiments. CF3SF5 is a possible choice since it is very similar to SF6 in terms of its properties, techniques for injection, sampling, and analysis.
Experiments were conducted by David Y. Ho, James R. Ledwell, and William M. Smethie Jr. to test the potential use of CF3SF5 for ocean tracer release experiments. These researchers injected a mixture containing the tracers, SF6, and CF3SF5 into the Santa Monica Basin and San Pedro Basin at depths of 800 meters. The mixture of tracers was sampled one week, 5 months, 12 months, and 23 months after injection. The samples showed the dispersion of the tracers throughout the Santa Monica Basin and San Pedro Basin over time. The samples were then analyzed using a gas chromatograph equipped with an electron capture detector. The results indicated that CF3SF5 and SF6 tracked each other nearly identically for the 5 month, 12 month, and 23 month samples, signifying that CF3SF5 can be used as an alternate tracer to SF6. CF3SF5 can currently replace SF6 for injectable tracer release experiments; however its diffusion coefficient needs to be measured before it can be used in gas exchange experiments (1).
CF3SF5 is considered to be one of the most potent greenhouse gases in the atmosphere on a per molecule basis. Its global warming potential is approximately 18,000 times the global warming potential of carbon dioxide. Its ability to cause global warming can be attributed to the wavelengths of light that it absorbs. The most effective greenhouse gases absorb light in the infrared range (700 to 1300 cm-1). CF3SF5 absorbs 60% of its light in the 800 to 1300 cm-1 range, making it a very efficient producer of global warming.
Th atmospheric lifetime of CF3SF5 is estimated to last 800 to 1000 years. For comparison, the lifetime of carbon dioxide is approximately 50 years. CF3SF5 lasts so long in the atmosphere because it is chemically inert. The most significant reactions that deplete CF3SF5 are electron attachment reactions. In these reactions, an electron attacks CF3SF5 to form an unstable intermediate that breaks apart. The concentration of CF3SF5 in the atmosphere is extremely low; however it is increasing steadily. Current concentrations are approximately 0.12 to 0.18 parts per trillion compared to a concentration of essentially zero prior to the 1960′s. The reasons for the increase in concentration are currently unknown, but are believed to be caused by human activity (2).
(1) Ho, D. T., J. R. Ledwell, and W. M. Smethie Jr. (2008), Use of SF5CF3 for ocean tracer release experiments, Geophys. Res. Lett., 35, L04602,doi:10.1029/2007GL032799.
(2) Suen, M (2008). Trifluoromethyl Sulfur Pentafluoride (CF3SF5): A Review of the Recently Discovered Super-Greenhouse Gas in the Atmosphere, The Open Atmospheric Science Journal, 2008, 2, 56-60.