MIPAS/Envisat Measurements Of SO2 From The Upper Troposphere To The Upper Stratosphere 2002-2012
Hoepfner, Michael1; Bruehl, Christoph2; Glatthor, Norbert1; Grabowski, Udo1; Kellmann, Sylvia1; Kiefer, Michael1; Lelieveld, Jos2; Linden, Andrea1; Orphal, Johannes1; Stiller, Gabriele1; v. Clarmann, Thomas1
1Karlsruhe Institute of Technology, GERMANY; 2Max-Planck-Institute for Chemistry, GERMANY
Sulphur dioxide (SO2) is one of the key species determining the aerosol content of the stratosphere. Apart from this study, only three measured profiles of SO2 concentrations (by ATMOS) covering the altitude range of the stratosphere have been published, two of which are heavily perturbed by the Pinatubo eruption and one by El Chichon. Here we present a climatology of monthly and 10deg zonal mean profiles of SO2 volume mixing ratios in the altitude range 15-45 km as derived from MIPAS/Envisat measurements from July 2002 until April 2012. The vertical resolution varies from 3.5-4 km in the lower stratosphere up to 6-10 km at the upper end of the profiles with estimated total errors of 5-20 pptv for background conditions of SO2. Comparisons are made with few available observations of SO2 up to high altitudes from ATMOS, for volcanically perturbed situations in the lower stratosphere from ACE-FTS and at the lowest altitudes with stratospheric in-situ observations. The dataset proves for the first time several features of the stratospheric SO2 distribution, which up to now, have only been shown by models: (1) the local maximum of SO2 at around 25-30 km altitude from conversion of COS as the pre-curser of the Junge layer and (2) the downwelling of SO2-rich air to altitudes of 25-30 km at high latitudes during winter and its subsequent depletion during spring as cause for the sudden appearance of enhanced concentrations of condensation nuclei. Comparison with model results of SO2 from the SPARC aerosol assessment report indicate several inconsistencies between simulations and our observations. Further, dedicated runs with the chemistry-climate model EMAC reveal that the strong increase of SO2 to values of 80-100 pptv in the upper stratosphere can only be explained by taking into account visible and near-IR photolysis of H2SO4 and, in addition, a meteoritic sink. Lower stratospheric variability of SO2 can mainly be explained by volcanic activity. A modulation of the mid-stratospheric maximum could be observed for several equatorial eruptions during the time period of observations.