Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 3 2005 10.5194/acpd-5-3959-2005 http://www.atmos-chem-phys-discuss.net/5/3959/2005/ http://www.atmos-chem-phys-discuss.net/5/3959/2005/acpd-5-3959-2005.html http://www.atmos-chem-phys-discuss.net/5/3959/2005/acpd-5-3959-2005.pdf 3959 3998 2005-06-14 Piecewise log-normal approximation of size distributions for aerosol modelling K. von Salzen Canadian Centre for Climate Modelling and Analysis, Meteorological Service of Canada, Victoria, British Columbia, Canada An efficient and accurate method for the representation of particle size distributions in atmospheric models is proposed. The method can be applied, but is not necessarily restricted, to aerosol mass and number size distributions. A piecewise log-normal approximation of the number size distribution within sections of the particle size spectrum is used. Two of the free parameters of the log-normal approximation are obtained from the integrated number and mass concentration in each section. A third parameter is prescribed. The method is efficient in a sense that only relatively few calculations are required for applications of the method in atmospheric models. <br><br> Applications of the method to observed size distributions and simulations of nucleation, condensation, gravitational settling, and wet deposition with a single column model are described. The accuracy of the method is considerably higher than the accuracy of the frequently used bin method in these tests.