Remotely sensed measurements of sulphur dioxide (SO 2) emitted by Turrialba Volcano (Costa Rica) are reported for the period September 2009–January 2011. These measure-ments were obtained using images from Advanced Space-borne Thermal Emission and Reflexion radiometer, Ozone Monitoring Instrument and a ground-based UV camera. These three very different instruments provide flux measurements in good agreement with each other, which demonstrate that they can be integrated for monitoring SO 2 fluxes. Fluxes from Turrialba increased fourfold in January 2010, following a phreatic explosion that formed a degassing vent in the W crater of Turrialba. Since then, the SO 2 flux has remained high (30–50 kg/s) but seems to be showing a slowly decreasing trend. We interpret this evolution as the start of open vent degassing from a recently intruded magma body. The opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrother-mal system.