The contribution of explosive volcanism to global atmospheric sulphur dioxide concentrations

Abstract

SULPHUR dioxide from volcanic eruptions may have a significant effect on the Earth's climate and atmospheric chemistry, and it is therefore important to quantify outgassing rates for all types of volcanic activity. Non-explosive volcanoes (for example, Mount Etna) outgas at relatively constant rates, providing an annual flux of about 9 million tons (Mt) SO₂ (ref. 1). By contrast, the outgassing from volcanoes prone to explosive eruptions (such as Mount Pinatubo) is sporadic and much more difficult to quantify. The total annual volcanic SO₂ flux is therefore poorly constrained, with ground-based estimates^1–8 ranging from 1.5 to 50 Mt–up to onequarter of the estimated current anthropogenic contribution. The Total Ozone Mapping Spectrometer aboard the NASA satellite Nimbus 7 recorded SO₂emissions from explosive eruptions from November 1978 to May 1993. We use these data to show that the annual flux from explosive volcanism is of the order of 4 Mt SO₂, less than half of the non-explosive output. Thus it seems that the total volcanic emission of SO₂ to the Earth's atmosphere is about 13 Mt yr⁻¹, which is only 5–10% of the current anthropogenic flux.