Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 3 2006 10.5194/acpd-6-3465-2006 http://www.atmos-chem-phys-discuss.net/6/3465/2006/ http://www.atmos-chem-phys-discuss.net/6/3465/2006/acpd-6-3465-2006.html http://www.atmos-chem-phys-discuss.net/6/3465/2006/acpd-6-3465-2006.pdf 3465 3512 2006-05-04 MALTE – Model to predict new aerosol formation in the lower troposphere M. Boy O. Hellmuth H. Korhonen E. D. Nilsson D. ReVelle A. Turnipseed F. Arnold M. Kulmala Department of Physical Sciences, Division of Atmospheric Sciences, P.O. Box 64, 00014 University of Helsinki, Finland ASP/ACD, NCAR, P.O. Box 3000, 80305 Boulder, Colorado, USA Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20 E, FIN-00880 Helsinki, Finland Department of Meteorology, Stockholm University, S-106 91 Stockholm, Sweden Earth and Environmental Sciences, Los Alamos National Laboratory, P.O. Box 1663, MS D401, Los Alamos, NM, 87545, USA ACD, NCAR, P.O. Box 3000, 80305 Boulder, Colorado, USA Atmospheric Physics Division, Max-Planck Institute for Nuclear Physics, (MPIK), P.O. Box 103980, 69029 Heidelberg, Germany The manuscript presents a detailed description of the meteorological and chemical code of Malte – a model to predict new aerosol formation in the lower troposphere. The aerosol dynamics are achieved by the new developed UHMA (University of Helsinki Multicomponent Aerosol Model) code with kinetic limited nucleation as responsible mechanism to form new clusters. First results indicate that the model is able to predict the on- and offset of new particle formation as well as the total aerosol number concentrations that were in good agreement with the observations. Further, comparison of predicted and measured H₂SO₄ concentrations showed a satisfactory agreement. The simulation results indicated that at a certain transitional particle diameter (2–9 nm), organic molecules can begin to contribute significantly to the growth rate compared to sulphuric acid. At even larger particle sizes, organic molecules can dominate the growth rate on days with significant monoterpene concentrations. The intraday vertical evolution of newly formed clusters and particles in two different size ranges resulted in two maxima at the ground and the top of the mixed layer with higher concentrations for the detectable particles above 3 nm below in contrast to the predicted cluster concentrations.