A numerical scheme for the advection part of a small-scale mathematical-meteorological model developed earlier is proposed. The algorithm has a technical advantage when dealing with implicit difference schemes. The flow produced by the meteorological model serves as a basis for the calculation of pollutant transport over complex terrain. A simple Monte Carlo method is used for this purpose. Some results of a calculation for the transport of a passive substance over a steep hill are presented. A reasonably good agreement with the existing theory is achieved.