A Lagrangian approach for the simulation of atmospheric dispersion of passive, nonbuoyant, and nonreactive tracers in a turbulent flow. Particle trajectories are calculated by assuming the evolution of turbulent velocities to be Markovian (thus experiencing an acceleration of partly stochastic nature). One-particle models assume the particles to be independent of each other and thus are able to predict ensemble-average statistics only. Two-particle models take into account the relative movement of particle pairs and can therefore predict concentration fluctuations and hence provide information on the actual realization of a plume of pollutants.