Comparison of volcanic outgassing simulations and measurements from the Mt. Etna volcanic plume

Characterization of the emitted volcanic gas composition provides crucial information about the processes that affect the volatile magmatic constituents during the degassing process. In the present study, we compare measurements collected from the Etna volcanic plume with simulations of the chemical evolution of the outgassed volatiles. To simulate the composition of the volcanic plume for the COHS system, we developed a numerical model that reproduces the different steps of volatile outgassing from the silicate melt to the atmosphere. First, we identify the possible initial volatile contents using data from melt/fluid inclusions from the literature and we simulate the solubility of the volatile species by considering different pressures, temperatures and redox states of the system. Once the volatiles are exsolved, we determine their chemical speciation assuming thermochemical equilibrium between the melt and the gas phase. In the final step of our simulation, we model the chemical evolution during the mixing of the hot volcanic plume with atmospheric air based on high-temperature reactions. To evaluate the oxidation state of the volcanic plume, we compare the CO/CO₂ ratio of measured and simulated compositions. We note that the final outgassed composition could mirror the oxidation state and the temperature of the host melt but it could also be affected by chemical conversions at the magma-atmosphere interface in the first seconds after gas release. By using this approach, we reconstruct the potential chemical evolution of the volatile composition during the entire volcanic degassing process, linking the simulated and measured compositions of the Mt Etna volcanic plume.