Observations of volcanic SO₂ from MLS on Aura

Abstract. Sulfur dioxide (SO₂) is an important atmospheric constituent, particularly in the aftermath of volcanic eruptions. These events can inject large amounts of SO₂ into the lower stratosphere, where it is oxidised to form sulfate aerosols; these in turn have a significant effect on the climate. The MLS instrument on the Aura satellite has observed the SO₂ mixing ratio in the upper troposphere and lower stratosphere from August 2004 to the present, during which time a number of volcanic eruptions have significantly affected those regions of the atmosphere. We describe the MLS SO₂ data and how various volcanic events appear in the data. As the MLS SO₂ data are currently not validated we take some initial steps towards their validation. First we establish the level of internal consistency between the three spectral regions in which MLS is sensitive to SO₂. We compare SO₂ column values calculated from MLS data to total column values reported by the OMI instrument. The agreement is good (within about 1 DU) in cases where the SO₂ is clearly at altitudes above 147 hPa.