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| Titel |
Quantifying HCl and SO2 adsorption by tephra in volcanic eruptions |
| VerfasserIn |
Paul Martin Ayris, Pierre Delmelle, Elena Maters, Donald Bruce Dingwell |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074133
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| Zusammenfassung |
| Tephra-gas interaction in eruption plumes leads to scavenging of volatiles (SO2, HCl, HF)
and forms soluble salts and aqueous acids on tephra surfaces. The presence of these
compounds may induce a number of environmental effects upon tephra emission and
deposition. These may range from acid damage to vegetation surfaces, to the release of key
nutrients or toxic metals into lake or surface ocean waters. It has also been suggested that
alterations to tephra surface chemistry imparted by volatile scavenging may contribute to
in-plume particle aggregation, so influencing tephra dispersal and fallout. Gaining
further insight into the possible effects associated with, or indirectly resulting from,
gas-tephra interaction necessitates a renewed mechanistic investigation of the latter.
Such an undertaking must expand upon the three stage, ‘solid aerosol adhesion /
volatile adsorption / acid condensation’ scavenging model proposed by Oskarsson
in 1980. We present the results of SO2 and HCl uptake experiments on tephrite,
phonolite, dacite and rhyolite glass powders conducted over a range of in-plume
temperatures (100-800Ë C). Using a suite of analytical techniques, we identified coupled
adsorption-diffusion mechanisms driving the scavenging of SO2 and HCl. These
volatiles reacted with Ca- and Na-bearing surface sites to form CaSO4, Na2SO4
and NaCl deposits; uptake is thought to be sustained respectively by near-surface
co-diffusion of O2- with Ca2+ or Na+, and interdiffusion between H+ and Na+. The
scavenging of SO2 and HCl was also subject to complex thermal, temporal and
compositional controls which were strongly influenced by the chemical composition of the
glass. By reference to our experimental findings and to current plume evolution and
conduit flow models, we are able to estimate the potential for SO2 and HCl uptake by
direct adsorption onto tephra particles within the eruption plume. Our findings
therefore highlight those eruptive environments where in-plume gas adsorption
may significantly alter tephra surface chemistry, and in doing so, may dictate the
intensity of any induced chemical effects in the plume or in receiving environments. |
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