Ash iron mobilization through physicochemical processing in volcanic eruption plumes: a numerical modeling approach

Abstract

Abstract. It has been shown that volcanic ash fertilizes the Fe-limited areas of the surface ocean through releasing soluble iron. As ash iron is mostly insoluble upon the eruption, it is hypothesized that heterogeneous in-plume and in-cloud processing of the ash promote the iron solubilization. Direct evidences concerning such processes are, however, lacking. In this study, a 1-D numerical model is developed to simulate the physicochemical interactions of the gas-ash-aerosol in volcanic eruption plumes focusing on the iron mobilization processes at temperatures between 600 and 0 • C. Results show that sulfuric acid and water vapor condense at ∼ 150 and ∼ 50 • C on the ash surface, respectively. This liquid phase then efficiently scavenges the surrounding gases (> 95 % of HCl, 3-20 % of SO 2 and 12-62 % of HF) forming an extremely acidic coating at the ash surface. The low pH conditions of the aqueous film promote acid-mediated dissolution of the Fe-bearing phases present in the ash material. We estimate that 0.1-33 % of the total iron available at the ash surface is dissolved in the aqueous phase before the freezing point is reached. The efficiency of dissolution is controlled by the halogen content of the erupted gas as well as the mineralogy of the iron at ash surface: elevated halogen concentrations and presence of Fe 2+ -carrying phases lead to the highest dissolution efficiency. Findings of this study are in agreement with the data obtained through leaching experiments.

Photochemical box-modelling of volcanic SO<sub>2</sub> oxidation: isotopic constraints

“…For all the simulations LWC is set to 1.0 gr m −3 , a value between experimental measurements (e.g. meteorological clouds) and modelling studies of water-rich volcanic plumes reaching the upper troposphere (Tabazadeh and Turco, 1993;Hoshyaripour et al, 2015). Like SO 2 , LWC is found to be a critical model input.…”

“…Fig:10 (Maters et al, 2016). According to the measurements, concentration of dissolved [Fe(III)] generally varies in the range of 0.1 to 2 µ M depending on the 10 mineral composition (Hoshyaripour et al, 2015;Maters et al, 2016). However, there is a lot of uncertainty on the typical concentrations of dissolved iron mobilized in volcanic plumes.…”

“…Particular attention has been paid recently to this heterogeneous oxidation pathway, since its contribution could have been underestimated in previous budget assessments of sulphate production in the troposphere (Alexander et al, 2009;Goto et al, 2011;Harris et al). During eruptive events, volcanoes emit large quantities of ash and coarse material rich in ironminerals (mainly glass, and in lesser extents magnetite and hematite), which can easily dissolve in water because of the high acidity reached in volcanic cloud droplets and aerosols (Ayris and Delmelle, 2012;Hoshyaripour et al, 2015;Maters et al, 5 2016). As a consequence, the O 2 /TMI heterogeneous oxidation reaction may be more significant than previously thought.…”

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…The co-absorption of H 2 O and HCl is the main reason for the generation of volcanic ash particle coats containing soluble-Fe salts originating from insolubleFe oxides and Fe silicates (Hoshyaripour et al, 2015;Martin et al, 2012). Gaseous HCl from the eruption plume entails Fe chlorides covering the surfaces of volcanic ash particles (Ayris et al, 2014).…”

An Adaptive Semi-Lagrangian Advection Model for Transport of Volcanic Emissions in the Atmosphere

“…(Bagheri and Bonadonna, 2016)) and complex chemical reactions which could occur between different trace gases in the atmosphere while being transported (e.g. (Hoshyaripour et al, 2015))…”