<div class="page" title="Page 1"><div class="layoutArea"><div class="column"><p><span>Mt. Etna volcano in Italy is one of the most active degassing volcanoes worldwide, emitting a mean of 1.7 Mt/year of Sulphur Dioxide (SO</span><span>2</span><span>) in quiescent periods. In this work, SO</span><span>2 </span><span>measurements retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS), hyper-spectral Infrared Atmospheric Sounding Interferometer (IASI) and the second Global Ozone Monitoring Experiment (GOME-2) data are compared with the ground-based data from the FLux Automatic MEasurement monitoring network (FLAME). Among the eighteen lava fountain episodes occurring at Mt. Etna in 2011, the 10 April paroxysmal event has been selected as a case-study for the simultaneous observation of the SO</span><span>2 </span><span>cloud by satellite and ground-based sensors. For each data-set two retrieval techniques were adopted and the measurements of SO</span><span>2 </span><span>mass and flux with their respective uncertainty were obtained. With respect to the FLAME SO</span><span>2 </span><span>mass of 4.5 Gg, MODIS, IASI and GOME-2 differ by about 10%, 15% and 30%, respectively. The SO</span><span>2 </span><span>flux correlation coefficient between MODIS and FLAME is 0.84. All the retrievals within the respective errors are in agreement with the ground-based measurements supporting the validity of these space measurements. </span></p></div></div></div>