While sulfate tends to be a dominant compound (by mass) in volcanic submicron particles , PM0.95sulfate proxy may still significantly underestimate the total submicron particle mass if the observed plumes were rich in primary volcanic ash. While we cannot precisely quantify the contribution of primary volcanic ash because key ash constituents, like silicon oxides, aluminium oxides, or iron oxides, were not measured, its contribution to volcanic submicron particle mass is expected to lie between 0 and 50% after some plume aging has occurred . In fact, for most eruptions from Piton de la Fournaise very low content of fine ash was reported 59 .