Dispersion

This WP aims at increasing our knowledge on volcanic plumes dispersion at several spatio-temporal scales and inherent impacts. The spatial scales span from near-source to regional and global scales. Source emission properties of the particle-gas mixture strongly influence the physico-chemical evolution in the atmosphere of the resulting cloud. These activities thus involve consideration of a variety of processes taking place over time scales spanning seconds to years, if we consider climatic impacts. WP3 will focus on the study of the mixture of gaseous species and particle types that are present within the volcanic plume. The particles mixture may contain juvenile and non-juvenile lapilli to ash particles, sulfur-rich aerosols and hydrometeors (ice particles and liquid water droplets). These span a range of sizes from a few centimeters (ash, hydrometeors) down to a few microns (fine mode ash and secondary aerosols in accumulation mode) and nanometers (secondary aerosols in nucleation mode). The gas mixture is mainly composed of H2O, CO2 and SO2, and also halogenated compounds (e.g. HBr, HCl, HF, BrO, ClO, OClO, etc).

From the point of view of atmospheric sciences, the ultimate goal is to better understand atmospheric impacts, including environmental impacts on air quality, health, air traffic, ozone depletion and, on the long-term, on global atmospheric composition and climate forcing. With this new knowledge, it would be possible to improve our current forecast capabilities of volcanic cloud dispersal and atmospheric/climatic responses. In addition, we propose to gather a large set of observations to assess the robustness of model simulations for volcanic cloud dispersal at the different temporal and spatial scales.

For both volcanology and atmospheric science communities, it is critical to constrain the time evolution, the three-dimensional distribution and composition of the tephra/gas dispersal and sedimentation. Often, such observations and in-situ measurements are limited to proximal areas (a few km from the source). Secondly, it is essential to evaluate a complete and rigorous budget of total emission (gas + particle) from the vent source and their transfer to more distal locations. Finally, it is extremely important to link the dispersion process with conduit ascent and vent-exit dynamics (WP1 and WP2). In this regard, it is well-known that the fragmentation processes and conduit conditions (low viscosity versus high viscosity magma or magmatic versus phreatomagmatic processes) influences the resulting emission and this, in turn, is drives for plume ascent and plume dispersion. Secondary processes (i.e. particle-particle collision, secondary fragmentation and aggregation; lightening) can potentially modify the particle size distribution and particle properties and their influence need to be better quantified and integrated in the models.

In order to constrain and attribute the pollution related to volcano degassing, the complex processes occurring during and after mixing with other sources of aerosol (natural or anthropogenic) need to be quantified and modeled, extending the attribution work made for some some test volcanoes like Mt. Etna (Sellitto et al., 2017a), and possibly linking this attribution to pollution/climate impacts.