Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 1 2005 10.5194/acpd-5-179-2005 http://www.atmos-chem-phys-discuss.net/5/179/2005/ http://www.atmos-chem-phys-discuss.net/5/179/2005/acpd-5-179-2005.html http://www.atmos-chem-phys-discuss.net/5/179/2005/acpd-5-179-2005.pdf 179 215 2005-01-14 A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties D. V. Spracklen K. J. Pringle K. S. Carslaw M. P. Chipperfield G. W. Mann The School of Earth and Environment, University of Leeds, UK A GLObal Model of Aerosol Processes (GLOMAP) has been developed as an extension to the TOMCAT 3-D Eulerian off-line chemical transport model. GLOMAP simulates the evolution of the global aerosol size distribution using a sectional two-moment scheme and includes the processes of aerosol nucleation, condensation, growth, coagulation, wet and dry deposition and cloud processing. We describe the results of a global simulation of sulfuric acid and sea spray aerosol. The model captures features of the aerosol size distribution that are well established from observations in the marine boundary layer and free troposphere. Modelled condensation nuclei (CN>3 nm) vary between about 250–500 cm^-3 in remote marine boundary layer regions and between 2000 and 10 000 cm^-3 (at standard temperature and pressure) in the upper troposphere. Cloud condensation nuclei (CCN) at 0.2% supersaturation vary between about 1000 cm^-3 in polluted regions and between 10 and 500 cm^-3 in the remote marine boundary layer. New particle formation through sulfuric acid-water binary nucleation occurs predominantly in the upper troposphere, but the model results show that these particles contribute greatly to aerosol concentrations in the marine boundary layer. It is estimated that sea spray emissions account for only ~10% of CCN in the tropical marine boundary layer, but between 20 and 75% in the mid-latitude Southern Ocean.