Reactive halogen chemistry in volcanic plumes

Abstract

[1] Bromine monoxide (BrO) and sulphur dioxide (SO 2 ) abundances as a function of the distance from the source were measured by ground-based scattered light Multiaxis Differential Optical Absorption Spectroscopy (MAX-DOAS) in the volcanic plumes of Mt. Etna on Sicily, Italy, in August-October 2004 and May 2005 and Villarica in Chile in November 2004. BrO and SO 2 spatial distributions in a cross section of Mt. Etna's plume were also determined by Imaging DOAS. We observed an increase in the BrO/SO 2 ratio in the plume from below the detection limit near the vent to about 4.5 Â 10 À4 at 19 km (Mt. Etna) and to about 1.3 Â 10 À4 at 3 km (Villarica) distance, respectively. Additional attempts were undertaken to evaluate the compositions of individual vents on Mt. Etna. Furthermore, we detected the halogen species ClO and OClO. This is the first time that OClO could be detected in a volcanic plume. Using calculated thermodynamic equilibrium compositions as input data for a one-dimensional photochemical model, we could reproduce the observed BrO and SO 2 vertical columns in the plume and their ratio as function of distance from the volcano as well as vertical BrO and SO 2 profiles across the plume with current knowledge of multiphase halogen chemistry, but only when we assumed the existence of an ''effective source region,'' where volcanic volatiles and ambient air are mixed at about 600°C (in the proportions of 60% and 40%, respectively).

The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) – a novel imaging DOAS device for 2-D and 3-D imaging of trace gases and aerosols

“…During a campaign in July 2011, the volcanic emission plume of Mount Etna (Sicily, Italy) was mapped, showing BrO / SO 2 ratios of about 1.5 ×10 −4 . This value is in good agreement with prior measurements by e.g., Vogel (2011) or Bobrowski et al (2007. Further flights were conducted in the metropolitan area of Indianapolis (Indiana, USA) in fall of the same year.…”

“…I-DOAS techniques are well established in remote sensing and were successfully used in many applications in the past. For instance, BrO formation in volcanic plumes has been studied using ground-based I-DOAS measurements (e.g., Louban, 2005;Bobrowski et al, 2007). On a larger scale, satellite data have been used to quantify the strength of ship emissions based on SCIA-MACHY NO 2 distribution patterns in the Indian Ocean or emission from cities .…”

Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna's emissions

“…Thermodynamic models have been used in a number of recent studies to model the compositional changes occurring as hot magmatic gases mix and react with cold atmospheric gases at volcanic vents (e.g., Gerlach, 2004;Martin et al, 2006;Bagnato et al, 2007;Bobrowski et al, 2007;Martin et al, 2009b). The assumption in these models is that magmatic and atmospheric gases equilibrate instantaneously at the vent until a temperature (typically N500°C) is reached where the composition becomes frozen (i.e., the quenching temperature).…”

Atmospheric chemistry in volcanic plumes

“…This view changed recently, mainly because of the observation of very high concentrations of bromine oxide, BrO, in the tropospheric, nonexplosive plume of Soufrière Hills, Montserrat (1). Since then, an increasing number of observations of reactive halogens have been made in noneruptive plumes of various volcanoes (2)(3)(4). Many more measurements of the early plumes of various craters including the chemical composition of aerosol (5) in recent years showed many more facets of the exciting chemical processes in noneruptive volcanic plumes.…”

“…The model setup is based on observations for Mount Etna, Sicily, during nonexplosive stages (3,7,8,9). The crater altitude of the modeled volcano is 3,300 m; the modeled plume is noncondensing.…”