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UP: Umweltphysik

UP 26: Atmosph
äre und Aerosole: Datenauswertung und Modellierung

UP 26.1: Fachvortrag

Wednesday, March 15, 2006, 14:30–14:45, E

Model sensitivity studies on atmospheric iodine chemistry and coastal nucleation events — •Susanne Pechtl and Roland von Glasow — Institut für Umweltphysik, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany

We perform sensitivity studies regarding atmospheric iodine chemistry, and the possible role of iodine oxides in atmospheric new particle formation. We use the one-dimensional marine boundary layer model MISTRA, which includes chemistry in the gas and aerosol phase as well as aerosol microphysics. The chemical reaction set focuses on halogen (Cl-Br-I) chemistry. We considered both ternary sulfuric acid - ammonia - water nucleation and homomolecular homogeneous OIO nucleation. For the latter, we derived a parameterization based on combined laboratory - model studies. According to these sensitivity studies, in the clean marine background atmosphere OIO can be responsible for both homogeneous nuclei formation and the subsequent growth of the clusters to detectable sizes. In contrast to this, in the continental case with its higher levels of pollutants nucleation rates are significantly lower. Compared to ternary H2SO4-NH3-H2O nucleation, homogeneous OIO nucleation can be neglected for new particle formation in this case, but OIO can contribute to early particle growth. In general, we found OIO to be more important for the growth of newly formed particles than for the formation of new nuclei itself. There are still considerable uncertainties regarding iodine chemistry in the atmosphere as well as the exact mechanism of new particle formation via iodine oxides. We discuss sensitivity studies adressing some of these uncertainties.