HR: 14:52h
AN: A43F-05    [Abstracts]
TI: The influence of organic coatings on water evaporation rates from aqueous ammonium sulphate aerosols
AU: * Kiendler-Scharr, A
EM: a.kiendler-Scharr@fz-juelich.de
AF: Forschungszentrum Juelich, Leo Brandt Strasse 1, Juelich, 52425 Germany
AU: Mentel, T F
EM: t.mentel@fz-juelich.de
AF: Forschungszentrum Juelich, Leo Brandt Strasse 1, Juelich, 52425 Germany
AB: An open issue related to organic aerosol components is their ability to form films around atmospheric particles, i.e. if and how aqueous particles get coated with water-insoluble material. Organic aerosol formation resulting from ozonolysis of α-pinene, myrcene and sabinene was investigated in a large aerosol chamber in the presence of aqueous seed aerosols. The partitioning of oxidation products into the aerosols was observed to exhibit a clear size dependence such that smaller particles contained relatively more organics than larger ones. This is interpreted as indication for an organic coating on the aqueous seed aerosols. Aerosol chemical composition was measured with an Aerodyne Aerosol Mass spectrometer (AMS). The measured and expected particulate water are compared. For that the expected mole fraction of water was calculated based on measured inorganic composition of the aerosol and the relative humidity in the aerosol chamber. For the pure inorganic seed aerosols the measured water mole fractions were generally about 50% of the expected. The observed water loss can be explained by evaporation of water when particles pass the aerodynamic lens system of the AMS instrument. The rise in the organic aerosol component after ozone addition is accompanied by a steep increase in the water content of the particles. This leads to almost 90% of the expected water being detected by the AMS. Our observations are interpreted as the result of the organic coating on the particles which hinders the evaporation of water during the passage of the aerodynamic lens. Thus organic coatings may additionally be of atmospheric relevance if they are able to delay equilibration of the particles with gas phase water in fast transportation processes.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005