Atmospheric chemistry in volcanic plumes

Abstract

Recent field observations have shown that the atmospheric plumes of quiescently degassing volcanoes are chemically very active, pointing to the role of chemical cycles involving halogen species and heterogeneous reactions on aerosol particles that have previously been unexplored for this type of volcanic plumes. Key features of these measurements can be reproduced by numerical models such as the one employed in this study. The model shows sustained high levels of reactive bromine in the plume, leading to extensive ozone destruction, that, depending on plume dispersal, can be maintained for several days. The very high concentrations of sulfur dioxide in the volcanic plume reduces the lifetime of the OH radical drastically, so that it is virtually absent in the volcanic plume. This would imply an increased lifetime of methane in volcanic plumes, unless reactive chlorine chemistry in the plume is strong enough to offset the lack of OH chemistry. A further effect of bromine chemistry in addition to ozone destruction shown by the model studies presented here, is the oxidation of mercury. This relates to mercury that has been coemitted with bromine from the volcano but also to background atmospheric mercury. The rapid oxidation of mercury implies a drastically reduced atmospheric lifetime of mercury so that the contribution of volcanic mercury to the atmospheric background might be less than previously thought. However, the implications, especially health and environmental effects due to deposition, might be substantial and warrant further studies, especially field measurements to test this hypothesis

SO2photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

“…The actinic flux used in the model does not consider any alterations to radiative conditions of stratosphere caused by the plume itself, but the actinic flux spectrum will vary due to the particular radiative conditions to a given eruption. In addition, although the concentration of SO 2 of several parts per million is similar to the concentration assumed by Savarino et al (7), it is lower than the concentration in the initial plume described in a recent plume model (31). We ignored initial plume chemistry, including heterogeneous chemistry, to focus on homogeneous chemistry in the stratosphere, which is important globally.…”

Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna's emissions

“…Low temperature kinetic modelling of Etna's emissions (von Glasow, 2010) suggests that, within 15 min of emission, Hg(0) (i.e., GEM) may be oxidised completely to Hg(II) (i.e., RGM + Hg p ) by Br and Cl radicals. The source of these Br and Cl radicals is thought to be high temperature chemistry occurring as magmatic and atmospheric gases mix and react at Etna's vents (Bagnato et al, 2007).…”

“…Early studies have reported much higher RGM + Hg p , including N60% of Hg tot at Etna (DeDeurwaerder et al, 1982) and 80% of Hg tot at Erebus, Antarctica (McMurtry et al, 1979). The process and extent of Hg deposition has yet to be studied in any detail and remains a key unknown, although is likely influenced by the initial Hg speciation (i.e., Hg tot = GEM + RGM + Hg p ) (von Glasow, 2010).…”

Ultraviolet Imaging of Volcanic Plumes: A New Paradigm in Volcanology

“…Considerably more follow-on work would be required in order to establish whether calibrated and therefore quantitatively meaningful outputs could be achieved from this measurement approach. A further possible research focus relates to the capacity of the cameras to image rates of volcanic gas-ambient air mixing, which are known to exert a key control on plume bromine monoxide (BrO) chemistry [65,66]. To date, the atmospheric chemistry modeling approaches applied to investigate this phenomenon have been based on assumed Gaussian-type plume dispersion scenarios.…”