Emission and composition of aerosols in the volcanic plume of Masaya volcano, Nicaragua.

Masaya Volcano, Nicaragua, has been passively degassing since 1993. This gas crisis provides a unique opportunity for investigating the degassing of magmatic volatiles. Here, we studied the chemical composition of the volcanic particulate phase collected directly from the plume. The objective was to gain new insights into the volatilities and emission rates of trace elements. The results indicate enrichments in the aerosol phase of all analyzed trace elements, including not only those known to be volatile (such as Cu and Te) but also elements considered as refractory (such as Rare Earth Elements (REEs) and Th). REEs were fractionated with a significant enrichment of Light Rare Earth Elements (LREEs) over Heavy Rare Earth Elements (HREEs). This pattern suggests degassing of LREEs as chlorides. In general, the emission of most trace elements in volcanic plumes is governed by the primary degassing of chloride compounds. However, SEM-EDS data and chemical analysis of aerosol filters allow us to state that trace elements can also be released as sulphate and chloro-sulphate compounds. The trace element emission rates at Masaya are significant and place this volcano as a major gas emitter. However, for some elements like Cu, Masaya's contribution to the global volcanic flux seems disproportionate, probably pointing to the poor dataset available for other degassing volcanoes.