Retrieval of sulphur dioxide from the infrared atmospheric sounding interferometer (IASI)

Abstract. Thermal infrared sounding of sulphur dioxide (SO₂) from space has gained appreciation as a valuable complement to ultraviolet sounding. There are several strong absorption bands of SO₂ in the infrared, and atmospheric sounders, such as AIRS (Atmospheric Infrared Sounder), TES (Tropospheric Emission Spectrometer) and IASI (Infrared Atmospheric Sounding Interferometer) have the ability to globally monitor SO₂ abundances. Most of the observed SO₂ is found in volcanic plumes. In this paper we outline a novel algorithm for the sounding of SO₂ above ~5 km altitude using high resolution infrared sounders and apply it to measurements of IASI. The main features of the algorithm are a wide applicable total column range (over 4 orders of magnitude, from 0.5 to 5000 dobson units), a low theoretical uncertainty (3–5%) and near real time applicability. We make an error analysis and demonstrate the algorithm on the recent eruptions of Sarychev, Kasatochi, Grimsvötn, Puyehue-Cordón Caulle and Nabro.