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Sensitivity of aerosol concentrations and cloud properties to nucleation and secondary organic distribution in ECHAM5-HAM global circulation model
1Department of Physics, University of Helsinki, FI-00014, Helsinki, Finland
2Department of Physics, University of Kuopio, FI-70211, Kuopio, Finland
3Max Planck Institute for Meteorology, D-20146, Hamburg, Germany
4Finnish Meteorological Institute, FI-00101, Helsinki, Finland
5Finnish Meteorological Institute, FI-70211, Kuopio, Finland
6Institute of Atmospheric and Climate Science, ETH Zurich, CH-8092, Zurich, Switzerland
†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 lower troposphere. A simple and computationally efficient model for biogenic secondary organic aerosol (BSOA) formation was implemented. We studied the sensitivity of 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 2×10-7 s−1, 2×10-6 s-1 and 2×10-5 s−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 dynamic SOA scheme induces large regional changes to size distribution of organic carbon, and therefore affects particle optical properties and cloud droplet number concentrations locally. Comparison with satellite observation shows that activation-type nucleation significantly decreases the differences between observed and modeled values of cloud top CDNC.
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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., 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. Discuss., 8, 10955-10998, 2008. Bibtex EndNote Reference Manager
