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

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.