Observations of volcanic SO2 from MLS on Aura

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.