SO2/BrO ratios studied in five volcanic plumes

The distribution of bromine monoxide (BrO) and sulphur dioxide (SO2) was measured by ground-based MAX DOAS (scattered light Multi Axis Differential Optical Absorption Spectroscopy) in the plume of five volcanoes:; Soufrière Hills Volcano on Montserrat in May 2002, Masaya volcano in Nicaragua in March 2003, Etna volcano on Sicily in September/October 2003 and August–October 2004, Stromboli volcano in Italy in September 2003, and Villarica in Chile in November 2004. Maximum slant column densities (SCDs) of several 1014 molecules/cm2 of BrO were observed. Bromine monoxide/sulphur dioxide ratios of 10.0 × 10− 4, 0.8 × 10− 4, 4.8 × 10− 4, 2.1 × 10− 4, 2.1 × 10− 4 and 1.3 × 10− 4 were found in the plumes of Soufrière Hills, Masaya, Etna 2003, Etna 2004, Stromboli and Villarica, respectively. Causes for the differences in the BrO/SO2 ratios for the various volcanic sites are discussed.