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Volume 16, issue 1 | Copyright

Special issue: The CERN CLOUD experiment (ACP/AMT inter-journal SI)

Atmos. Chem. Phys., 16, 293-304, 2016
https://doi.org/10.5194/acp-16-293-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 18 Jan 2016

Research article | 18 Jan 2016

Hygroscopicity of nanoparticles produced from homogeneous nucleation in the CLOUD experiments

J. Kim1,a, L. Ahlm2, T. Yli-Juuti1, M. Lawler1,3, H. Keskinen1,b, J. Tröstl4, S. Schobesberger5,c, J. Duplissy6, A. Amorim7, F. Bianchi4,8, N. M. Donahue9, R. C. Flagan10, J. Hakala11, M. Heinritzi12,13, T. Jokinen5, A. Kürten12, A. Laaksonen1,14, K. Lehtipalo5, P. Miettinen1, T. Petäjä5, M. P. Rissanen5, L. Rondo12, K. Sengupta15, M. Simon12, A. Tomé7,16, C. Williamson12, D. Wimmer5,8, P. M. Winkler17, S. Ehrhart12,18, P. Ye9, J. Kirkby12,18, J. Curtius12, U. Baltensperger4, M. Kulmala5, K. E. J. Lehtinen1,19, J. N. Smith1,3, I. Riipinen2, and A. Virtanen1 J. Kim et al.
  • 1Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 2Department of Applied Environmental Science, Stockholm University, Stockholm, Sweden
  • 3National Centre for Atmospheric Research, Boulder, CO 80305, USA
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • 5Department of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
  • 6Helsinki Institute of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
  • 7CENTRA-SIM, University of Lisbon, Lisbon, Portugal
  • 8Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland
  • 9Carnegie Mellon University, Center for Atmospheric Particle Studies, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA
  • 10California Institute of Technology, 210-41, Pasadena, CA 91125, USA
  • 11Division of Atmospheric Sciences, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
  • 12Goethe University of Frankfurt, Institute for Atmospheric and Environmental Sciences, Altenhöferallee 1, 60438 Frankfurt am Main, Germany
  • 13University of Innsbruck, Institute for Ion and Applied Physics, 6020 Innsbruck, Austria
  • 14Finnish Meteorological Institute, PL 501, 00101 Helsinki, Finland
  • 15University of Leeds, School of Earth and Environment, Leeds LS2 9JT, UK
  • 16University of Beira Interior, Beira, Portugal
  • 17Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
  • 18CERN, 1211 Geneva, Switzerland
  • 19Finnish Meteorological Institute, Kuopio Unit, Kuopio, Finland
  • anow at: Arctic research center, Korea Polar Research Institute, Incheon, South Korea
  • bnow at: Department of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
  • cnow at: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA

Abstract. Sulfuric acid, amines and oxidized organics have been found to be important compounds in the nucleation and initial growth of atmospheric particles. Because of the challenges involved in determining the chemical composition of objects with very small mass, however, the properties of the freshly nucleated particles and the detailed pathways of their formation processes are still not clear. In this study, we focus on a challenging size range, i.e., particles that have grown to diameters of 10 and 15nm following nucleation, and measure their water uptake. Water uptake is useful information for indirectly obtaining chemical composition of aerosol particles. We use a nanometer-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) at subsaturated conditions (ca. 90% relative humidity at 293K) to measure the hygroscopicity of particles during the seventh Cosmics Leaving OUtdoor Droplets (CLOUD7) campaign performed at CERN in 2012. In CLOUD7, the hygroscopicity of nucleated nanoparticles was measured in the presence of sulfuric acid, sulfuric acid–dimethylamine, and sulfuric acid–organics derived from α-pinene oxidation. The hygroscopicity parameter κ decreased with increasing particle size, indicating decreasing acidity of particles. No clear effect of the sulfuric acid concentration on the hygroscopicity of 10nm particles produced from sulfuric acid and dimethylamine was observed, whereas the hygroscopicity of 15nm particles sharply decreased with decreasing sulfuric acid concentrations. In particular, when the concentration of sulfuric acid was 5.1 × 106moleculescm−3 in the gas phase, and the dimethylamine mixing ratio was 11.8ppt, the measured κ of 15nm particles was 0.31±0.01: close to the value reported for dimethylaminium sulfate (DMAS) (κDMAS ∼ 0.28). Furthermore, the difference in κ between sulfuric acid and sulfuric acid–imethylamine experiments increased with increasing particle size. The κ values of particles in the presence of sulfuric acid and organics were much smaller than those of particles in the presence of sulfuric acid and dimethylamine. This suggests that the organics produced from α-pinene ozonolysis play a significant role in particle growth even at 10nm sizes.

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The hygroscopicity of nucleated nanoparticles was measured in the presence of sulfuric acid, sulfuric acid-dimethylamine, and sulfuric acid-organics derived from α-pinene oxidation during CLOUD7 at CERN in 2012. The hygroscopicity parameter κ decreased with increasing particle size, indicating decreasing acidity of particles.
The hygroscopicity of nucleated nanoparticles was measured in the presence of sulfuric acid,...
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