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An atmospheric photochemical source of the persistent greenhouse gas CF4
  • Published Date:

    2015

  • Source:
    Geophysical Research Letters, 42(21), 9505-9511.
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  • Description:
    A previously uncharacterized atmospheric source of the persistent greenhouse gas tetrafluoromethane, CF4, has been identified in the UV photolysis of trifluoroacetyl fluoride, CF3C(O)F, which is a degradation product of several halocarbons currently present in the atmosphere. CF4 quantum yields in the photolysis of CF3C(O) F were measured at 193, 214, 228, and 248 nm, wavelengths relevant to stratospheric photolysis, to be (75.3 +/- 1) x 10(-4), (23.7 +/- 0.4) x 10(-4), (6.6 +/- 0.2) x 10(-4), and <= 0.4 x 10(-4), respectively. A 2-D atmospheric model was used to estimate the contribution of the photochemical source to the global CF4 budget. The atmospheric photochemical production of CF4 from CF3CH2F (HFC-134a), CF3CHFCl (HCFC-124), and CF3CCl2F (CFC-114a) per molecule emitted was calculated to be (1-2.5) x 10(-5), 1.0 x 10(-4), and 2.8 x 10(-3), respectively. Although CF4 photochemical production was found to be relatively minor at the present time, the identified mechanism demonstrates that long-lived products with potential climate impacts can be formed from the atmospheric breakdown of shorter-lived source gases.
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