In the course of three measuring trips to the Mt. Etna volcano (Sicily), field measurements and measurements by aircraft were carried out in the plume of the volcano to determine the concentration distributions and emission rates for the sulfur compounds H2S, SO2, and SO42-. Furthermore, the removal of H2S and SO2 and the production of SO42- in the dispersing plume were investigated. The dispersion of the plume was studied by simultaneous tracer measurements of the CO2 concentration. H2S was additionally measured at the crater rims of Stromboli and Vulcano. The sulfur source strength of Mt. Etna was considerably dependent on the activity phase which was post-eruptive and pre-eruptive, respectively. The emission rates were found to vary between 142--1600 t SO2/d, 1--10 t H2S/d and 182--232 t SO42-/d. Oxidation rates of 1.7--5.0¿10-4 s-1 for SO2 and 2.1¿10-4 s-1 for H2S could be determined by the application of two different theoretical models which are described in detail.