A fast and efficient modified sectional method for simulating multicomponent collisional kinetics

A fast and efficient method for simulating the evolution of internally mixe d multicomponent particle size distributions for aerosol coagulation and dr oplet coalescence is developed. The technique is based upon a bin-wise sect ionalization of the particle mass domain and by imposing the condition of m ass conservation for each component. The distribution of each species as a function of the total particle mass is represented in each mass bin as a tw o-parameter exponential function. Particles of a given mass are assumed to be internally homogeneously mixed. The method is shown to be numerically st able for a wide range of time steps. The numerical solution is compared wit h both analytical results and results from other well-accepted numerical sc hemes. This comparison reveals that the proposed technique offers the advan tage of being fast and accurate, even for coarse spectral resolution. The m ethod is computationally attractive and easily allows the treatment of ten or more different chemical species in a collisionally evolving particle siz e distribution. The applicability of the method is demonstrated with severa l examples: Coalescence growth of multicomponent cloud droplet spectra, coa gulation of measured multi-species aerosol particle size distributions, and the simulation of the accumulation mode due to a source of small aerosol p articles. The technique is ideally suited for modelling the interaction of microphysics and chemistry in a size-bin resolving aerosol or cloud model. (C) 1999 Elsevier Science Ltd. All rights reserved.