Aerosol formation in basaltic lava fountaining: Eyjafjallajökull volcano, Iceland



[1] A short-lived episode of basaltic lava fountaining at Eyjafjallajökull volcano (March – April 2010) produced a low-altitude, ash-poor plume. We measured the composition of aerosol particles (sampled using a cascade impactor and filter packs), gases (sampled using filter packs), and volatile species scavenged by scoria and external water in order to investigate the formation and speciation of near-source aerosol (<2 min from emission). Samples were analyzed for volatile species (S, Cl and F) and metals (Na, K, Ca and Mg). The aerosol mass showed two unusual features: the prevalent size mode was finer than typically found in volcanic plumes (∼0.2μm, compared to >0.4 μm), and its composition was dominated by chloride rather than sulfate. We used two thermodynamic equilibrium models (E-AIM and HSC Chemistry v5.1) to show that the formation of particulate Cl by condensation of HCl gas is more responsive to changes in ambient temperature than the oxidation of SO2 to SO42−, so that a low SO42−/Cl ratio in aerosol particles is characteristic of volcanic emissions in cold climates. Field measurements suggested that the efficiency of SO2 to SO42− conversion inside the vent increased with lower explosivity. Volatiles adsorbed on the surface of scoria had significantly higher SO42−/halogen molar ratios than the aerosol samples. Several potential explanations for these differences are discussed.