Temporal variations of flux and altitude of sulfur dioxide emissions during volcanic eruptions: implications for long-range dispersal of volcanic clouds

Abstract

Abstract. Sulfur-rich degassing, which is mostly composed of sulfur dioxide (SO 2 ), plays a major role in the overall impact of volcanism on the atmosphere and climate. The accurate assessment of this impact is currently hampered by the poor knowledge of volcanic SO 2 emissions. Here, using an inversion procedure, we show how assimilating snapshots of the volcanic SO 2 load derived from the Infrared Atmospheric Sounding Interferometer (IASI) allows for reconstructing both the flux and altitude of the SO 2 emissions with an hourly resolution. For this purpose, the regional chemistry-transport model CHIMERE is used to describe the dispersion of SO 2 when released in the atmosphere. As proof of concept, we study the 10 April 2011 eruption of the Etna volcano (Italy), which represents one of the few volcanoes instrumented on the ground for the continuous monitoring of SO 2 degassing.We find that the SO 2 flux time-series retrieved from satellite imagery using the inverse scheme is in agreement with ground observations during ash-poor phases of the eruption. However, large discrepancies are observed during the ashrich paroxysmal phase as a result of enhanced plume opacity affecting ground-based ultraviolet (UV) spectroscopic retrievals. As a consequence, the SO 2 emission rate derived from the ground is underestimated by almost one order of magnitude.Altitudes of the SO 2 emissions predicted by the inverse scheme are validated against an RGB image of the Moderate Resolution Imaging Spectroradiometer (MODIS) capturing the near-source atmospheric pathways followed by Etna plumes, in combination with forward trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. At a large distance from the source, modelled SO 2 altitudes are compared with independent information on the volcanic cloud height. We find that the altitude predicted by the inverse scheme is in agreement with snapshots of the SO 2 height retrieved from recent algorithms exploiting the high spectral resolution of IASI. The validity of the modelled SO 2 altitude is further confirmed by the detection of a layer of particles at the same altitude by the spaceborne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Analysis of CALIOP colour and depolarization ratios suggests that these particles consist of sulfate aerosols formed from precursory volcanic SO 2 .The reconstruction of emission altitude, through inversion procedures which assimilate volcanic SO 2 column amounts, requires specific meteorological conditions, especially sufficient wind shear so that gas parcels emitted at different altitudes follow distinct trajectories. We consequently explore the possibility and limits of assimilating in inverse schemes infrared (IR) imagery of the volcanic SO 2 cloud altitude which will render the inversion procedure independent of the wind shear prerequisite.

New strategies for vertical transport in chemistry-transport models: application to the case of the Mount Etna eruption on March 18, 2012 with CHIMERE v2017r4

“…In order to analyse atmospheric diffusion, the Etna eruption of March 18, 2012 has been modelled using the CHIMERE CTM in the aim to propose and test strategies to improve representation of atmospheric vertical diffusion which has previously been described in multiple studies (Colette et al, 2011;Boichu et al, 2015;Mailler et al, 2017, e.g. ) as over-diffusing, inducing an excessive spread of the simulated plumes.…”

“…Several parameters can influence the evolution of the modelled plume: the emission fluxes and time profile; the injection height and vertical profile; chemical processes involving the considered species; the wind field; the numerical advection schemes and the vertical resolution. Boichu et al (2015) have focused on volcanic plume dispersion sensitivity to altitude of injection, combining CHIMERE and Atmospheric Sounding Interferometer instrument (IASI) for a Mount Etna -study case of an eruption of moderate intensity in April 2011. The eruption presented an emission profile centered at 7 000 m.a.s.l., with weaker emissions at 4 000 m.a.s.l..…”

Synergistic use of Lagrangian dispersion and radiative transfer modelling with satellite and surface remote sensing measurements for the investigation of volcanic plumes: the Mount Etna eruption of 25–27 October 2013

“…Salerno et al, 2009a). It is well known that matching between ground-and satellite-based SO 2 emissions estimations might display large discrepancies, due to plume height uncertainties, and sulfate aerosol, ash and ice in the volcanic plume, which may introduce over-or underestimation of the SO 2 burden in both ground-and satellite-based retrievals (Boichu et al, 2015, and references therein). A direct comparison of the estimates from the two methods is beyond the scope of this study; instead we employ the groundbased SO 2 emissions for classifying the magnitude of the 26 October episode.…”

Apport de l'observation satellitaire à l'analyse et à la prévision de la qualité de l'air

“…Des concentrations particulièrement élevées ont ainsi été mesurées par Iasi lors des grands feux de l'automne 2015 qui ont ravagé l'Indonésie suite à la sécheresse intense liée à un épisode El Niño (figure 2b). Chazette et al, 2012 ;Boichu et al, 2015). , ont montré des capacités pour restituer la distribution verticale des aérosols dits grossiers (typiquement pour un diamètre supérieur à 1 µm) comme les poussières minérales (Cuesta et al, 2015).…”