The speciation of Hg in volcanic plumes is less studied than total Hg emissions and is thus subject to even larger uncertainties . This is problematic, as the fate of Hg in volcanic plumes and its environmental impact depends importantly on Hg speciation and in-plume transformations. Gaseous elemental mercury (GEM) is water-insoluble and thus not significantly removed from the atmosphere by wet deposition. Reactive mercury, on the other hand, whether in the gas phase as gaseous oxidized mercury (GOM) or attached to particles as particle-bound mercury (PBM), is considerably more water-soluble than GEM, making it subject to significant wet deposition. In addition, reactive mercury tends to have significantly larger dry deposition velocities than GEM . GEM consequently has a relatively long atmospheric lifetime (i.e. e-folding time) of ~ 6 -12 months which allows for global circulation and dispersal , while GOM and PBM have much shorter lifetimes (hours to days) and thus more regional impacts through localized deposition.