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Composition and size characterisation of volcanic ash

Composition and size characterisation of volcanic ash. Gemma Prata Supervisors: Tamsin Mather and David Pyle. Clarisse et al. 2010. Refractive index influence on retrievals. Francis et al. 2012, JGR. Eyjafjallajökull , 13 th May 2010. 1.5% Hematite dust Balkanski et al. 2007.

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Composition and size characterisation of volcanic ash

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  1. Composition and size characterisation of volcanic ash Gemma Prata Supervisors: Tamsin Mather and David Pyle

  2. Clarisse et al. 2010

  3. Refractive index influence on retrievals Francis et al. 2012, JGR

  4. Eyjafjallajökull, 13th May 2010 1.5% Hematite dust Balkanski et al. 2007 Andesite Pollack et al. 1973 Obsidian Pollack et al. 1973 Volcanic dust (basalt?) Volz 1973 Francis et al. 2012, JGR

  5. Particle size measurement Malvern Mastersizer 2000 Size range: 0.02 – 2000 µm Uses Mie and Fraunhofer scattering Mie: requires sample refractive index Fraunhofer: refractive index not required Need about a teaspoon of sample

  6. Particle size distributions

  7. Effect of size distribution Volume percentage

  8. Bulk composition – XRF

  9. Individual component composition – Microprobe

  10. Size-resolved and internal composition – QEMSCAN

  11. Individual component composition Size-resolved composition Bulk composition

  12. X-Ray Fluorescence(XRF) • quick and easy • bulk composition • assumes no size dependence of composition Melt whole sample Quench to glass

  13. Electron Probe Microanalysis(EPMA) • gives composition at specific points • user selects points • beam diameter 10 µm

  14. Glass vs. bulk composition

  15. QEMSCAN Example from Etna 2006 Colour key: Sulphates (purple) Silicates (green, blue, pink) Sulphur/sulphides (yellow, claret) Martin et al. 2008, JGR

  16. Complex index of refraction: n*  =  n + i · k n – real part k– imaginary part Literature values compiled from Narcisi & Vezzoli, Global and Planetary Change, 1999 P < 0.05

  17. Questions?

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