Registration Dossier
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EC number: 219-854-2 | CAS number: 2551-62-4
Phototransformation in air
Administrative data
Link to relevant study record(s)
Description of key information
The degradation rate coefficient for reaction of SF6 with O(1D) was estimated to be 1.5E-14 cm3/mol/s.
Key value for chemical safety assessment
Additional information
The atmospheric lifetime of SF6 was estimated by Ravishankara et al. (1993). The reaction of SF6 with O(1D) and the photolysis mediated by Lyman radiation were considered as the possible degradation pathways. The OH-mediated photodegradation was considered as not relevant by the authors.
The degradation rate coefficient for reaction of SF6 with O(1D) was estimated to be 1.5E-14 cm3/mol/s. Experiments with Lyman alpha-radiation showed an absorption cross section of 1.76 ± 13 E-18 cm2. Although the fate of the excited SF6, formed by the absorption of the Lyman radiation, was not investigated, the molecule dissociation into F- and SF5+ was assumed to occur, due to the high energy of the absorbed radiation.
A global atmospheric lifetime of 3,200 years was calculated for SF6. According to the authors, only the 24% of SF6 removal takes place in the troposphere through Lyman alpha-radiation mediated photolysis. The main process of removal of SF6 from the troposphere was identified to be its advection into mesosphere, where the substance may be subjected to degradation via the reaction with free electrons.
The Intergovernmental Panel on Climate Change (2001) listed SF6 with a global warming potential of 22200 on a 100 year time horizon relative to CO2, by considering the global atmospheric lifetime of 3200 years and a radiative forcing of 0.52 Wm-2ppb-1.
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