Heidelberg 1999 – wissenschaftliches Programm
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UP: Umweltphysik
UP 11: Poster: Atmosphärenphysik und Physikalische Altersbestimmung
UP 11.30: Poster
Freitag, 19. März 1999, 12:45–14:30, KO
Simultaneous measurements of of gaseous sulfuric acid and SO2 in the upper troposphere and lower stratosphere: Implications for the formation and growth of aerosol particles — •K.-H. Wohlfrom, J. Curtius, B. Sierau, J. Schneider, and F. Arnold — MPI for nuclear physics, Atmospheric physics division, P.O. Box 103980, D-69029 Heidelberg
Simultaneous measurements of gaseous sulfuric acid and SO2 have been carried out by aircraft borne Ion-Molecule Reaction Mass Spectrometry (IMRMS) at altitudes between 8 and 13 km. Gaseous sulfuric is produced photochemically in the atmosphere from its precursor SO2 and plays an important role for the formation and growth of aerosol particles. Direct sources of SO2 are mostly anthropogenic emissions, and it is also poduced from oxidation of organic sulfur species in the atmosphere. Measurements performed at sunrise over the Atlantic Ocean show an increase of the gaseous sulfuric acid number density with solar zenith angle. Measurements in the tropopause region at midlatitudes reveal SO2 mixing ratios of 50 to 150 pptV in the upper troposphere and only 10 to 50 pptV in the lower stratosphere. Corresponding gaseous sulfuric acid number densities in the upper troposphere are 5 × 105 to 2.5 × 106 cm−3 and decrease to 1 × 105 to 5 × 105 cm−3 in the lower stratosphere. Both gases show a positive correlation with a ratio of gaseous sulfuric acid to SO2 of 0.001 to 0.002. The measured partial pressure of gaseous sulfuric acid is high enough to reach saturation with respect to a flat surface of 98 % liquid sulfuric acid. Because of the very much lower saturation vapour pressure of a sulfuric acid-water solution this indicates that the formation of sulfuric acid-water aerosols via homogeneous bi-molecular H2SO4-H2O nucleation is possible in these regions of the atmosphere.