The hypothesis: Particle-induced GEM depletion Ermolin et al. (2018) 77 separated volcanic nanoparticles (< ~100 nm in at least one dimension) from settled bulk ash and analysed them for trace metals, finding that they had very elevated Hg mass fractions of 9 -36 PPM (1 PPM = 1 µg Hg /g particle ), corresponding to an enrichment factor of up to ~450 with respect to the earth's crust (Hg mass fraction ~ 0.08 PPM) . The authors suggested that a strong accumulation of trace elements like Hg occurs in the course of a volcanic eruption and upon plume dilution. In another study, coincident observations of PBM (~100 pg m -3 ) and suspended particles below 2.5 µm in diameter (PM2.5; ~12.5 µg m -3 ) in a ~10 days aged volcanic plume suggest a similarly elevated particle Hg mass fraction of ~ 8 PPM 80 . To our knowledge, no other study investigated Hg in fine particles (defined here as ≤ 10 µm in diameter) of volcanic origin, be it on settled particles or within a volcanic plume.