Size dependent partitioning of organic material: evidence for the formation of organic coatings on aqueous aerosols |
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Authors: | T Anttila A Kiendler-Scharr Th F Mentel R Tillmann |
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Institution: | 1.ICG-2: Troposph?re, Forschungszentrum Jülich,Jülich,Germany;2.Finnish Meteorological Institute, Research and Development, Climate and Global Change,Helsinki,Finland |
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Abstract: | Organic aerosol formation resulting from the ozonolysis of α-pinene, myrcene and sabinene was investigated in a large aerosol
chamber in the presence of aqueous seed aerosols. The chemical composition of the particles was monitored by an aerosol mass
spectrometer (Aerodyne Research Inc.) as a function of time and the particle size. Smaller particles were found to contain
more organics relative to sulfate than the larger ones. In contrast, the water to sulfate mass ratio was not dependent on
the particle size. These experimental findings indicate the formation of organic layers on the particles. With the aid of
an aerosol dynamic model we demonstrate that the observations are consistent with the formation of multilayered organic films
having thicknesses of approximately 10 nm. The results also suggest that the films were formed through condensation of low-volatile
oxidation products that did not take up water considerably. Even though dissolution of oxidation products into the particle
aqueous phase cannot be conclusively ruled out, the most plausible interpretation of the results is that the monoterpene ozonolysis
lead to the formation of organic coatings on aqueous aerosols. Such films are likely to form in regions with monoterpene emissions. |
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Keywords: | Aerosol dynamic modeling Aerosol mass spectrometer Organic films Secondary organic aerosol |
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