ABSTRACT. In this study a powerful tool to investigate the permeabilities and effective diffusion coefficients of polar firn is presented using a combination of an experimental method for three dimensional pore structure reconstruction and two models to simulate advective and diffusive transports of gases through the pore space. The reconstruction follows a semi-automated digital analysis of serial surface sections. The simulations are based on a three-dimensional lattice Boltzmann formulation. They separately solve the Navier-Stokes equation and the diffusive transport equations. In a first application effective diffusion coefficients and permeabilities are calculated from firn samples of a core drilled during the North-Greenland-Traverse 1993-95. The estimated relationships of diffusivity and permeability to the open porosity are expressed by power law functions with exponents 2.1 and 3.4, respectively.