ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-12-4525-2012 Hygroscopic growth and droplet activation of soot particles: uncoated, succinic or sulfuric acid coated Henning S. 1 Ziese M. 1 5 Kiselev A. 1 6 Saathoff H. 2 Möhler O. 2 Mentel T. F. 3 Buchholz A. 3 Spindler C. 3 Michaud V. 4 Monier M. 4 Sellegri K. 4 Stratmann F. 1 Institute for Tropospheric Research, 04318 Leipzig, Germany Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany Forschungszentrum Jülich, 52425 Jülich, Germany Laboratoire de Météorologie Physique, Université Blaise Pascal, 63177 Aubière Cedex, France now at: Deutscher Wetterdienst, 63067 Offenbach/M., Germany now at: Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany 24 05 2012 12 10 4525 4537 Copyright: © 2012 S. Henning et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/12/4525/2012/acp-12-4525-2012.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/12/4525/2012/acp-12-4525-2012.pdf

The hygroscopic growth and droplet activation of uncoated soot particles and such coated with succinic acid and sulfuric acid were investigated during the IN-11 campaign at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility. A GFG-1000 soot generator applying either nitrogen or argon as carrier gas and a miniCAST soot generator were utilized to generate soot particles. Different organic carbon (OC) to black carbon (BC) ratios were adjusted for the CAST-soot by varying the fuel to air ratio. The hygroscopic growth was investigated by means of the mobile Leipzig Aerosol Cloud Interaction Simulator (LACIS-mobile) and two different Hygroscopicity Tandem Differential Mobility Analyzers (HTDMA, VHTDMA). Two Cloud Condensation Nucleus Counter (CCNC) were applied to measure the activation of the particles. For the untreated soot particles neither hygroscopic growth nor activation was observed at a supersaturation of 1%, with exception of a partial activation of GFG-soot generated with argon as carrier gas. Coatings of succinic acid lead to a detectable hygroscopic growth of GFG-soot and enhanced the activated fraction of GFG- (carrier gas: argon) and CAST-soot, whereas no hygroscopic growth of the coated CAST-soot was found. Sulfuric acid coatings led to an OC-content dependent hygroscopic growth of CAST-soot. Such a dependence was not observed for activation measurements. Coating with sulfuric acid decreased the amount of Polycyclic Aromatic Hydrocarbons (PAH), which were detected by AMS-measurements in the CAST-soot, and increased the amount of substances with lower molecular weight than the initial PAHs. We assume that these reaction products increased the hygroscopicity of the coated particles in addition to the coating substance itself.

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