Emission of bromine and iodine from Mount Etna volcano

Abstract

[1] Constraining fluxes of volcanic bromine and iodine to the atmosphere is important given the significant role these species play in ozone depletion. However, very few such measurements have been made hitherto, such that global volcanic fluxes are poorly constrained. Here we extend the data set of volcanic Br and I degassing by reporting the first measurements of bromine and iodine emissions from Mount Etna. These data were obtained using filter packs and contemporaneous ultraviolet spectroscopic SO 2 flux measurements, resulting in time-averaged emission rates of 0.7 kt yr À1 and 0.01 kt yr À1 for Br and I, respectively, from April to October 2004, from which we estimate global Br and I fluxes of order 13 (range, 3-40) and 0.11 (range, 0.04-6.6) kt yr À1 . Observed changes in plume composition highlight the coherent geochemical behavior of HCl, HF, HBr, and HI during magmatic degassing, and strong fractionation of these species with respect to SO 2 .

Reactive halogen chemistry in volcanic plumes

“…[37] These observation suggest an enrichment of halogens at the NE crater (or a depletion of SO 2 ) in comparison with the Voragine crater and Bocca Nova; this is also supported by routine filter pack measurements carried out over 2004 [Aiuppa et al, 2005].…”

“…The wind data suggest that it is possible that the plume of the NE crater influenced the May 2005 measurements more than the measurements carried out in September and October 2004. As shown above and by Aiuppa et al [2005], the NE crater is, relative to SO 2 , richer in halogen compounds than, for instance, Voragine. (squares) and SO 2 (dots) are plotted over the telescope elevation angle of the telescope.…”

“…600°C. The HSC software uses a freeenergy minimization algorithm in order to calculate the molecular equilibrium composition of a gas mixture, given its starting elemental composition, T and p. We show model runs for different initial elemental compositions formed by variable mixtures of volcanic gases and ambient air, where Etna's volcanic gas composition (H 2 O, 78%; CO 2 , 8.7%; SO 2 , 2.6%; HCl, 1.3%; HBr, 0.006%) is from Aiuppa et al [2005] and additional calculations with HSC. Furthermore, we compare model runs based on this data with a run based on the numbers from Gerlach [2004] for mean compositions of arc volcanoes at 900°C (''arc mean'') with a mixture of 85% plume air and 15% background air for several types of volcanoes.…”

“…Nevertheless, it has been shown by thermodynamic models that significant amounts of atomic halogen species (i.e., Cl, Br) can be produced by high-temperature oxidative dissociation in a volcanic gas-air mixture [Gerlach, 2004;Aiuppa et al, 2005;Martin et al, 2006], particularly above the so-called compositional discontinuity, at which drastic changes in the speciation of gases occur [Gerlach and Nordlie, 1975]. The subsequent dilution of the volcanic gas-air mixture with ambient air leads to the entrainment of O 3 and HO x at the plume edges promoting the onset of autocatalytic radical reactions, including the oxidation of atomic species (XO, X = I, Br, Cl), in particular bromine:…”

“…[7] As suggested by field studies and numerical simulations [Francis et al, 1995[Francis et al, , 1998Gerlach, 2004;Aiuppa et al, 2005], halogens are mainly emitted by volcanoes as hydrogen halides (e.g., HCl, HBr). Nevertheless, it has been shown by thermodynamic models that significant amounts of atomic halogen species (i.e., Cl, Br) can be produced by high-temperature oxidative dissociation in a volcanic gas-air mixture [Gerlach, 2004;Aiuppa et al, 2005;Martin et al, 2006], particularly above the so-called compositional discontinuity, at which drastic changes in the speciation of gases occur [Gerlach and Nordlie, 1975].…”