Mercury from volcanoes: fluxes and speciation

Mercury is a toxic bio-accumulating metal that, due to its volatility has an extended atmospheric lifetime. Understanding Hg sources and sinks is therefore has importance on the global scale. We present new measurements of volcanic Hg from Mount Etna and Vulcano in Italy and Masaya volcano in Nicaragua to improve our estimates of the volcanic Hg flux. In contrast to other metals emitted from volcanoes, volcanic Hg can exist in 3 forms, namely gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and in the particle phase. These measurements also represent the first fully speciated measurements of volcanic Hg, as well as the first high time resolution measurements of gaseous Hg. Volcanic Hg is primarily emitted as GEM with about 1- 5% present in the particles and about 1% by mass present as RGM. Hg/SO ratios at the 3 2 -5 -6 volcanoes were generally of order 10 to 10 suggesting that global volcanic Hg flux, from -1 degassing basaltic volcanoes, could be of the order of 74 Mg yr . At Masaya Hg/C ratios were also determined at low temperature fumaroles. These low temperature Hg fluxes were found to be insignificant at Masaya; consistent with the dominance of high temperature degassing fluxes for other volatile species at Masaya (e.g. SO , CO ). Much more work remains to be done to 2 2 understand the roles of magma composition, eruptive temperature and volcanic gas composition in determining the SO – Hg – CO systematics of magmatic gases. 2 2