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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 5 | Copyright

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

Atmos. Chem. Phys., 9, 1747-1766, 2009
https://doi.org/10.5194/acp-9-1747-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  09 Mar 2009

09 Mar 2009

Sensitivity of aerosol concentrations and cloud properties to nucleation and secondary organic distribution in ECHAM5-HAM global circulation model

R. Makkonen1, A. Asmi1, H. Korhonen2, H. Kokkola3, S. Järvenoja4,†, P. Räisänen4, K. E. J. Lehtinen2,5, A. Laaksonen2,5, V.-M. Kerminen4, H. Järvinen4, U. Lohmann6, R. Bennartz7, J. Feichter3, and M. Kulmala1 R. Makkonen et al.
  • 1Department of Physics, University of Helsinki, 00014, Helsinki, Finland
  • 2Department of Physics, University of Kuopio, 70211, Kuopio, Finland
  • 3Max Planck Institute for Meteorology, 20146, Hamburg, Germany
  • 4Finnish Meteorological Institute, 00101, Helsinki, Finland
  • 5Finnish Meteorological Institute, 70211, Kuopio, Finland
  • 6Institute of Atmospheric and Climate Science, ETH Zurich, 8092, Zurich, Switzerland
  • 7Department of Atmospheric and Oceanic Sciences, University of Wisconsin, Madison, Wisconsin, USA
  • deceased, October 2007

Abstract. The global aerosol-climate model ECHAM5-HAM was modified to improve the representation of new particle formation in the boundary layer. Activation-type nucleation mechanism was introduced to produce observed nucleation rates in the lower troposphere. A simple and computationally efficient model for biogenic secondary organic aerosol (BSOA) formation was implemented. Here we study the sensitivity of the aerosol and cloud droplet number concentrations (CDNC) to these additions. Activation-type nucleation significantly increases aerosol number concentrations in the boundary layer. Increased particle number concentrations have a significant effect also on cloud droplet number concentrations and therefore on cloud properties. We performed calculations with activation nucleation coefficient values of 2×10−7s−1, 2×10−6s−1 and 2×10−5s−1 to evaluate the sensitivity to this parameter. For BSOA we have used yields of 0.025, 0.07 and 0.15 to estimate the amount of monoterpene oxidation products available for condensation. The hybrid BSOA formation scheme induces large regional changes to size distribution of organic carbon, and therefore affects particle optical properties and cloud droplet number concentrations locally. Although activation-type nucleation improves modeled aerosol number concentrations in the boundary layer, the use of a global activation coefficient generally leads to overestimation of aerosol number. Overestimation can also arise from underestimation of primary emissions.

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