The contribution of volcanoes to the global atmospheric sulfur budget

Abstract

A new assessment of the global volcanic emission rates of H 2 S, SO 2, and SO 42− is presented. The assessment is based on the development of a suitable classification of volcanic activity and its application to own measurements and measuring data given in the literature. Using this classification, the volcanic sulfur release is estimated to 1.18×10 7 t S/a total. This estimate must be regarded as a minimum since the data available for major explosive events are very uncertain. On the other hand the frequency of such events is comparatively low. We estimate a global volcanic emission of 1.52× 0 7 t SO 2/a for the period 1961–1979. Our calculations show that in this period the total SO 2 release during eruptive activities was at least 1.0×10 6 t SO 2/a whereas about 14 times as much, namely 1.42×10 7 t SO 2/a, were emitted during noneruptive activities. The importance of the contribution of the noneruptive activity has been neglected in earlier assessments. The average values for the global volcanic H 2 S and SO 42− source strength are found to be around 10 6 t/a and 10 7 t/a, respectively. We conclude that during a period of very intensive volcanic activity around the world, like that which recently has started with the eruptions of Soufrière in 1979 and Mount St. Helens in 1980, the global sulfur release during eruptive events may become up to 1 order of magnitude higher than we have calculated but that nevertheless the sulfur emission during the noneruptive activity is dominating.