• How the particle composition (e.g. sulfate content, halogen content, noble metals & transition metal oxides) may affect the capacity of volcanic aerosols to scavenge Hg requires further evaluation. This could either be achieved by adequate observations in a sufficiently aged volcanic plume or by the sampling of already settled volcanic particles (see Ermolin et al., 2018) 77 . In the latter case, it appears essential to size-segregate the particles. At the very least, fine particles (at least < 10 µm, but preferentially smaller) should be analysed separately from the bulk ash.