Annual contribution of sulfur dioxide to the atmosphere by volcanoes

The average contribution of SO₂ to the atmosphere by volcanoes, estimated largely by extrapolation from direct measurements of volcanic SO₂, is calculated to be 18.7 Tg per year. Of this, an estimated 6.8 Tg per year (36%) is from non-erupting degassing volcanoes. Erupting volcanoes yield an average annual flux estimated to be 11.9 Tg SO₂ per year (64%). The estimated total annual SO₂ output is about 23% larger than the most recent estimate based on direct measurements. Our calculations suggest that 64% of the total comes from erupting volcanoes, as compared to 7% in the earlier estimate. Of the total worldwide annual SO₂ flux, 9% is found to be from volcanoes.