This paper presents and applies a three-dimensional Monte Carlo transport and dispersion model applicable to individual plumes traveling over regional (>200 km) scales. Transport is explicitly calculated using a mass-consistent interpolated wind field. Dispersion is introduced solely by the interaction of vertical mixing and wind velocity shears. The degree of vertical mixing is parameterized contingent upon the Lagrangian time scale. The model was used to simulate the surface concentration of tracer released during the Cross-Appalachian Tracer Experiments (CAPTEX). The results indicate that the scale of horizontal distribution of tracer observed during the CAPTEX may be explained by the influence of vertical wind velocity shear. The simulations also suggest that the surface ''footprint'' did not represent well the movement of the majority of mass of the plumes for CAPTEX releases 1 and 2. The majority of the mass was simulated to have traveled to the south of the surface footprint and stayed well above the surface. Thus it is inappropriate to specify fixed-level trajectories as representative of the movement of pollutants over regional distances based on similarity of simulated to observed surface concentrations.