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Physico-chemical properties of tropospheric volcanic emissions

Physico-chemical properties of tropospheric volcanic emissions

Volcanoes are a major source of gases and particles to the atmosphere. Quantifying fluxes of volcanic gases, such as sulphur dioxide, is important for understanding the potential impacts on climate and local ecosystems, and hazards to human health. Sulphur dioxide emission is routinely monitored using ground-based and satellite remote sensing techniques to estimate fluxes and predict changes in eruptive activity. However, conversion rates of sulphur dioxide to sulphate aerosol are poorly constrained for tropospheric volcanic plumes, which can severely impact these measurements downwind from the volcano. Direct in situ measurement of volcanic emissions can be used to validate and improve remote sensing techniques. However, these data are sparse and the bulk of measurements comprise aircraft sampling carried out ~20-30 years ago, an approach now considered to be extremely hazardous.

New developments in sensor and communication technologies have led to the development of miniaturised light-weight unmanned airborne measurement platforms. Funding was secured by Dr Adam Durant with Paul Voss and Matt Watson through a U.S. National Science Foundation (NSF) Small Grants for Exploratory Research proposal (PI: Durant; EAR070602, $48,371) to perform a proof-of-concept study using state-of-the-art remotely-operated altitude-controlled meteorological (CMET) balloons as a platform to measure gases in volcanic plumes. These unique small balloons generate vertical profiles of atmospheric physical and chemical characteristics and can collect many hours of continuous data during a given flight.

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Paul Voss, developer of the CMET balloon platform, Smith College, MA, USA

As a component of the project, miniature gas sensors were added to the standard CMET balloon payload to measure sulphur dioxide and carbon dioxide concentrations in the atmosphere. Two successful CMET balloon flights were carried out in a volcanic plume during a field campaign at Kilauea volcano, Hawaii, in July 2008. This effort yielded the first in situ measurement of vertical profiles of volcanic plume sulphur dioxide, carbon dioxide and water vapour concentrations, and provided insights into down-wind evolution of sulphur dioxide in tropospheric volcanic plumes. The aim is to use the carbon dioxide concentration measurement as an inert tracer to account for plume mixing with the ambient atmosphere. Our overall goal is to constrain the rate of volcanic sulphur dioxide oxidation to sulphate aerosol in the troposphere.

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Launching a CMET balloon at Kilauea volcano, 25 July 2008 (image © John Catto)

This research featured in a National Geographic Television documentary, "Earth Report: State of the Planet 2009".