Natural sulfur dioxide emissions from sulfuric soils

Soils have long been recognised as sulfur dioxide (SO2) sinks, but we show that they can also be sources of atmospheric SO2. Using static chambers and micrometeorological techniques, we have measured emissions of SO2 from coastal lowland soils containing sulfides (mostly pyrite), commonly referred to as acid sulfate soils in Australia. SO2 evolution seems coupled to evaporation of soil water containing sulfite. The global emissions of S from acid sulfate soils is estimated at about 3 Tg/year, which is of the same order as emissions from terrestrial biogenic sources and biomass burning and is about 3% of known anthropogenic emissions of S.