HR: 09:45h
AN: A11C-08    [PDF]
TI: Influence Of Tropospheric OH On The Stratospheric Humidity And The Background Sulphuric Aerosol Layer: Impact Of Tropical Biomass Burning?
AU: * Notholt, J
EM: notholt@uni-bremen.de
AF: Institute of Environmental Physics, University of Bremen, Postfach 330440 Otto-Hahn-Allee, Bremen, 28334 Germany
AU: Weisenstein, D
EM: weisenstein@aer.com
AF: Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, MA 02421-3126 United States
AU: Lawrence, M
EM: lawrence@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, Department of Airchemistry, Postfach 3060, Mainz, 55020 Germany
AU: Rex, M
EM: mrex@AWI-Potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegraphenberg A43, Potsdam, 14473 Germany
AU: Peter, T
EM: thomas.peter@ethz.ch
AF: Institute for Atmospheric and Climate Science at the ETH, Hoenggerberg, Zuerich, 8093 Switzerland
AU: Luo, B
EM: luo@iac.umnw.ethz.ch
AF: Institute for Atmospheric and Climate Science at the ETH, Hoenggerberg, Zuerich, 8093 Switzerland
AU: von Kuhlmann, R
EM: kuhlmann@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, Department of Airchemistry, Postfach 3060, Mainz, 55020 Germany
AU: Warneke, T
EM: warneke@iup.physik.uni-bremen.de
AF: Institute of Environmental Physics, University of Bremen, Postfach 330440 Otto-Hahn-Allee, Bremen, 28334 Germany
AB: We propose a mechanism that couples stratospheric humidity and total sulphur levels in the stratosphere to the concentration of OH in the upper tropical troposphere. Our considerations are based on a 2-D sulphate aerosol model to calculate the number, surface and volume of particles formed in the atmosphere. The precursor gases considered are SO2, OCS, DMS, H2S and CS2. The microphysical processes simulated are homogeneous nucleation, condensation and evaporation, coagulation, and sedimentation. Recent observations and modelling studies indicate that HOx concentrations (OH + HO2) in the upper tropical troposphere are higher by a factor of two than previously assumed. Our model studies have been performed for two different OH-fields which differ by a factor of two in the upper tropical troposphere. The results show that the increase of OH significantly increases the formation of H2SO4 containing condensation nuclei in the upper tropical troposphere. Upon cooling to temperatures below the frost point the larger number of condensation nuclei leads to a slightly enhanced ice crystal number densities and, thus, to a slight reduction in the average ice particle size and sedimentation speed in the upper tropical troposphere. Therefore, on the average a larger fraction of these particles may be carried through the cold point tropopause by the rising motion of air, increasing the overall transport of water into the stratosphere. At the same time, an enhanced particle formation in the troposphere followed by some sedimentation decreases also to some extent the overall input of sulphur into the stratosphere. Since biomass burning is known to be a source of HOx, the long-term increase in the tropical burning activity could lead to increasing stratospheric humidity and a decreasing level of sulphur in the stratosphere.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere--composition and chemistry
DE: 1655 Water cycles (1836)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting