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 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
Citation: Makkonen, R., Asmi, A., Korhonen, H., Kokkola, H., Järvenoja, S., Räisänen, P., Lehtinen, K. E. J., Laaksonen, A., Kerminen, V.-M., Järvinen, H., Lohmann, U., Bennartz, R., Feichter, J., and Kulmala, M.: Sensitivity of aerosol concentrations and cloud properties to nucleation and secondary organic distribution in ECHAM5-HAM global circulation model, Atmos. Chem. Phys., 9, 1747-1766, doi:10.5194/acp-9-1747-2009, 2009.