Heidelberg 1999 – scientific programme

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UP: Umweltphysik

UP 11: Poster: Atmosphärenphysik und Physikalische Altersbestimmung

UP 11.11: Poster

Friday, March 19, 1999, 12:45–14:30, KO

Potential influence of the upper tropospheric trace gases sulfuric acid and nitric acid on aerosol particles and cirrus cloud formation: Measurements and Model calculations — •F. Arnold⁴, A. Laaksonen¹, L. Pirjola², M. Kulmala², F. Raes³, K.-H. Wohlfrom⁴, and F. Grimm⁴ — ¹Department of applied physics, University of Kuopio, Finnland — ²Department of physics, University of Helsinki, Finnland — ³Joint Research Center, Ispra, Italy — ⁴MPI for nuclear physics, Atmospheric physics division, P.O. Box 103980, D-69029 Heidelberg, Germany

Cirrus clouds are of considerable interest as they influence the earths radiation budget and climate. Cirrus clouds which cover 25-30 % of the earths surface are formed mostly in the upper troposphere via heterogeneous condensation of water vapour on aerosol particles. The latter are strongly influenced by gaseous sulfuric acid and nitric acid.

Gaseous sulfuric acid induces new particle formation via nucleation, and

particle growth via condensation. Gaseous nitric acid may dissolve in liquid H₂SO₄-H₂O aerosol particles and thereby reduce the equilibrium saturation H₂O-vapour pressure of these particles. Both condensational growth as well as HNO₃-uptake may activate a particle to become a cirrus cloud condensation nucleus.
Building on our aircraft measurements of gaseous sulfuric and nitric acid we have made model calculations to investigate the potential role of these trace gases in the formation of cirrus cloud condensation nuclei. We find that occasionally new particle formation via nucleation takes place and that freshly nucleated H₂SO₄-H₂O aerosol particles can undergo activation and therby contribute to cirrus cloud formation.