Articles | Volume 11, issue 23
Atmos. Chem. Phys., 11, 12369–12386, 2011

Special issue: European Integrated Project on Aerosol-Cloud-Climate and Air...

Atmos. Chem. Phys., 11, 12369–12386, 2011

Research article 09 Dec 2011

Research article | 09 Dec 2011

Aerosol hygroscopicity and CCN activation kinetics in a boreal forest environment during the 2007 EUCAARI campaign

K. M. Cerully1, T. Raatikainen2,3, S. Lance4,5, D. Tkacik6, P. Tiitta7,8, T. Petäjä9, M. Ehn9,*, M. Kulmala9, D. R. Worsnop3,7,9,10, A. Laaksonen3,7, J. N. Smith7,11, and A. Nenes1,2,12 K. M. Cerully et al.
  • 1School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
  • 2School of Earth and Atmospheric Science, Georgia Institute of Technology, Atlanta, GA, USA
  • 3Finnish Meteorological Institute, Helsinki, Finland
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 5Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 6Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USA
  • 7Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 8Atmospheric Chemistry Research Group, North-West University, Potchefstroom, South Africa
  • 9Department of Physics, University of Helsinki, Helsinki, Finland
  • 10Aerodyne Research Incorporated, Billerica, MA, USA
  • 11National Center for Atmospheric Research, Boulder, CO, USA
  • 12Institute of Chemical Engineering and High-Temperature Chemical Processes, Foundation for Research and Technology Hellas, Patras, Greece
  • *currently at: Institute for Energy and Climate Research, Forschungszentrum Jülich, Jülich, Germany

Abstract. Measurements of size-resolved cloud condensation nuclei (CCN) concentrations, subsaturated hygroscopic growth, size distribution, and chemical composition were collected from March through May, 2007, in the remote Boreal forests of Hyytiälä, Finland, as part of the European Integrated project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) campaign. Hygroscopicity parameter, κ, distributions were derived independently from Continuous Flow-Streamwise Thermal Gradient CCN Chamber (CFSTGC) and Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) measurements. CFSTGC-derived κ values for 40, 60, and 80 nm particles range mostly between 0.10 and 0.40 with an average characteristic of highly oxidized organics of 0.20 ± 0.10, indicating that organics play a dominant role for this environment. HTDMA-derived κ were generally 30% lower. Diurnal trends of κ show a minimum at sunrise and a maximum in the late afternoon; this trend covaries with inorganic mass fraction and the m/z 44 organic mass fraction given by a quadrupole aerosol mass spectrometer, further illustrating the importance of organics in aerosol hygroscopicity. The chemical dispersion inferred from the observed κ distributions indicates that while 60 and 80 nm dispersion increases around midday, 40 nm dispersion remains constant. Additionally, 80 nm particles show a markedly higher level of chemical dispersion than both 40 and 60 nm particles. An analysis of droplet activation kinetics for the sizes considered indicates that most of the CCN activate as rapidly as (NH4)2SO4 calibration aerosol.

Final-revised paper