The determination of microphysical aerosol parameters is an inverse, ill-posed problem. The shape and the material composition of the airborne particles are two substantial model parameters. Present evaluation algorithms only use the approximation of spherical, homogeneous particles. In this paper we propose a new numerically efficient recursive algorithm for spherically multilayered and absorbing particles. Numerical results of model particles show that the influence of the two parameters, i.e. shape and material composition, on the model is very important and cannot be ignored when inversion algorithms are used for determining microphysical parameters. (C) 2000 Elsevier Science Ltd. All rights reserved.