Assessment of the total emission of sulphur dioxide from Italian volcanoes in simultaneous shipborne measurements using lidar, doas and correlation spectroscopy

Volcanoes contribute substantial amounts of sulphur dioxide to the global atmosphere, and thus reliable measurements are needed for an accurate assessment of the relative roles of natural and antropogenic emissions. Normally, gas correlation measurements based on COSPEC instruments are performed, observing in ground-based traverses the spectral imprint of the gas in the spectrum of the down-welling ambient radiation. However, because of complicated scattering conditions above, within and below the volcanic plume, data are complex. The differential optical absorption spectroscopy (doas) technique works in a similar way but also provides the full spectrum for detailed analysis. The lidar technique, being an active remote sensing technique, provides more well-defined measurement conditions. Field tests have been performed using the research vessel "Urania", where scans under the plumes from the Italian volcanoes Etna, Stromboli and Volcano were performed. Three cruises were made, where the last one, in August 1997, provided the most complete and accurate data.