Volcanic ash in the atmosphere

Thesis

This thesis presents new work on the characterisation of volcanic ash in the atmosphere. The eruption of Eyjafjallajökull in 2010 brought the issue of ash in the atmosphere into sharp focus. Radiative transfer models used in remote sensing and hazard assessment of volcanic ash require knowledge of ash optical parameters, which are governed by the spectral complex refractive index (n + ik: where n is the real and k is the imaginary part). By investigating the relationship between volcanic ash composition and refractive index, a new parameterisation has been developed which will aid in the detection and quantification of hazardous ash clouds. It has been tested on retrievals from three recent eruptions using Infrared Atmospheric Sounding Interferometer (IASI) satellite data. The eruptions of Chaitén (Chile) in May 2008, Okmok (Aleutian Peninsula) in July 2008 and Grímsvötn (Iceland) in May 2011 allowed the testing and application of the parameterisation on a range of compositions, demonstrating that use of a parameterised index may significantly improve the retrieval of mass loading, a crucial parameter for assessing hazards to health, infrastructure and aviation. Direct sampling techniques are required to supplement satellite observations in order to ground-truth remote sensing techniques. A study of aerosol samples collected in the UK when the ash plume of Eyjafjallajökull was overhead has demonstrated that volcanic ash is chemically detectable above urban particulate matter, and that ash surface chemistry plays an important role in transporting heavy metals, which may have implications for remote sensing.

Authors: Prata, G

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Refractive index; Volcanic aerosols; Volcanic ash; Optical properties; Air quality; Chemical composition
• Subjects: Earth sciences; Volcanology; Remote sensing; Atmospheric physics