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

Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna’s emissions
Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna’s emissions
A major uncertainty regarding the environmental impacts of volcanic Hg is the extent to which Hg is deposited locally or transported globally. An important control on dispersion and deposition is the oxidation state of Hg compounds: Hg(0) is an inert, insoluble gas, while Hg(II) occurs as reactive gases or in particles, which deposit rapidly and proximally, near the volcanic vent. Using a new high temperature thermodynamic model, we show that although Hg in Etna's magmatic gases is almost entirely Hg(0) (i.e., gaseous elemental mercury), significant quantities of Hg(II) are likely formed at Etna's vents as gaseous HgCl2, when magmatic gases are cooled and oxidised by atmospheric gases. These results contrast with an earlier model study and allow us to explain recent measurements of Hg speciation at the crater rim of Etna without invoking rapid (< 1 min) low temperature oxidation processes. We further model Hg speciation for a series of additional magmatic gas compositions. Compared to Etna, Hg(II) production (i.e., Hg(II)/Hgtot) is enhanced in more HCl-rich magmatic gases, but is independent of the Hg, HBr and HI content of the magmatic gases. Hg(II) production is not strongly influenced by the initial oxidation state of magmatic gases above NNO, although production is hindered in more reduced magmatic gases. The model and results are widely applicable to other open-vent volcanoes and may be used to improve the accuracy of chemical kinetic models for low temperature Hg speciation in volcanic plumes.
Etna, Mercury, Hg, Volcano, Deposition
0009-2541
279-286
Martin, R.S.
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Witt, M.L.I.
99527c31-e719-4ec0-bddb-0c9226b50531
Pyle, D.M.
30f0cb90-7a4d-4219-9cff-1fabe2f0e4c1
Mather, T.A.
97b5dc46-dee8-4dcd-865f-d346fa0783ea
Watt, S.F.L.
76f594eb-9252-4a8b-822f-be71038b18db
Bagnato, E.
defd449c-25b9-4726-9fe1-b55b50e835e4
Calabrese, S.
641aacf9-4f04-423b-b02f-f52fd4732d3c
Martin, R.S.
0b02a657-2fe7-4d85-8d45-5eb77b8f3acc
Witt, M.L.I.
99527c31-e719-4ec0-bddb-0c9226b50531
Pyle, D.M.
30f0cb90-7a4d-4219-9cff-1fabe2f0e4c1
Mather, T.A.
97b5dc46-dee8-4dcd-865f-d346fa0783ea
Watt, S.F.L.
76f594eb-9252-4a8b-822f-be71038b18db
Bagnato, E.
defd449c-25b9-4726-9fe1-b55b50e835e4
Calabrese, S.
641aacf9-4f04-423b-b02f-f52fd4732d3c

Martin, R.S., Witt, M.L.I., Pyle, D.M., Mather, T.A., Watt, S.F.L., Bagnato, E. and Calabrese, S. (2011) Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna’s emissions. Chemical Geology, 283 (3-4), 279-286. (doi:10.1016/j.chemgeo.2011.01.027).

Record type: Article

Abstract

A major uncertainty regarding the environmental impacts of volcanic Hg is the extent to which Hg is deposited locally or transported globally. An important control on dispersion and deposition is the oxidation state of Hg compounds: Hg(0) is an inert, insoluble gas, while Hg(II) occurs as reactive gases or in particles, which deposit rapidly and proximally, near the volcanic vent. Using a new high temperature thermodynamic model, we show that although Hg in Etna's magmatic gases is almost entirely Hg(0) (i.e., gaseous elemental mercury), significant quantities of Hg(II) are likely formed at Etna's vents as gaseous HgCl2, when magmatic gases are cooled and oxidised by atmospheric gases. These results contrast with an earlier model study and allow us to explain recent measurements of Hg speciation at the crater rim of Etna without invoking rapid (< 1 min) low temperature oxidation processes. We further model Hg speciation for a series of additional magmatic gas compositions. Compared to Etna, Hg(II) production (i.e., Hg(II)/Hgtot) is enhanced in more HCl-rich magmatic gases, but is independent of the Hg, HBr and HI content of the magmatic gases. Hg(II) production is not strongly influenced by the initial oxidation state of magmatic gases above NNO, although production is hindered in more reduced magmatic gases. The model and results are widely applicable to other open-vent volcanoes and may be used to improve the accuracy of chemical kinetic models for low temperature Hg speciation in volcanic plumes.

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More information

Published date: 22 April 2011
Keywords: Etna, Mercury, Hg, Volcano, Deposition

Identifiers

Local EPrints ID: 190561
URI: http://eprints.soton.ac.uk/id/eprint/190561
ISSN: 0009-2541
PURE UUID: ca14e617-6127-48ed-9e50-d86b1354b377

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Date deposited: 21 Jun 2011 10:13
Last modified: 16 Jul 2019 23:28

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