Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

Abstract

Abstract.The interactions between triplet state benzophenone and halide anion species (Cl − , Br − and I − ) have been studied by laser flash photolysis (at 355 nm) in aqueous solutions at room temperature. The decay of the triplet state of benzophenone was followed at 525 nm. Triplet lifetime measurements gave rate constants, k q (M −1 s −1 ), close to diffusion controlled limit for iodide (∼8×10 9 M −1 s −1 ), somewhat less for bromide (∼3×10 8 M −1 s −1 ) and much lower for chloride (<10 6 M −1 s −1 ). The halide (X − ) quenches the triplet state; the resulting product has a transient absorption at 355 nm and a lifetime much longer than that of the benzophenone triplet state, is formed. This transient absorption feature matches those of the corresponding radical anion (X − 2 ). We therefore suggest that such reactive quenching is a photosensitized source of halogen in the atmosphere or the driving force for the chemical oxidation of the oceanic surface micro layer.

Quantifying the contribution of marine organic gases to atmospheric iodine

“…If, however, the additional I source were sunlight-dependent, such an accumulation of the precursor would not happen. Since neither I 2 nor other short-lived iodine precursors have been detected over the open ocean, it is not clear whether these emission rates are realistic, although experimental evidence demonstrates photochemical [Jammoul et al, 2009] and dark [Martino et al, 2009] production of I 2 (and VOICs) from surface seawater following ozone deposition to the surface. It should be noted however, that the levels of I 2 required to support the local IO concentrations are close to current instrument detection limits [Saiz-Lopez and Plane, 2004].…”

Iodine monoxide in the Western Pacific marine boundary layer

“…While mechanism (d) is already implemented in the MISTRA model, our study does not give hints as to whether mechanism (a) and (b) are more relevant for our observations and for open ocean iodine emissions in general. However, there are still uncertainties regarding e.g., the heterogeneous and aqueous phase processes, and the iodine release mechanism might be underpredicted by the model (e.g., Reeser et al, 2009;Jammoul et al, 2009). …”

Iodine chemistry in the eastern Pacific marine boundary layer

“…This suggests an inhibiting role of biological activity, although it must be noted that high Chl-a and CDOM are associated with upwelling of cold waters, and in fact they are seasonally anticorrelated to SST (to which IO x is positively correlated), which means that the aforementioned anticorrelation could be noncausal. In any case, a mechanism where the availability of dissolved organic matter or Chl-a is important [Reeser et al, 2008;Jammoul et al, 2009] (see also [Saiz-Lopez et al, 2012a]) would also be unlikely to dominate here.…”