It is well-known that particle inertia in dusty gas flows may cause a certain complex behavior of the concentration fields, such as the enrichment of particle concentration along particle trajectories. Traditional analyses of these and similar problems were made by treating the gas and the particles as two interpenetrating continua and using the two-phase flow equations for the description of the two phases. For cases with relatively low Stokes number, the concentration field may be obtained by a regular perturbation analysis of the equations of change using the Stokes number as a parameter. In the present study, we adopted the Lagrangian view of particle motion and obtained particle concentrations by applying mass balance to neighboring trajectories. In contrast to the earlier works, this approach can be used for all Stokes numbers and its application (at least in the cases considered) is straightforward. To demonstrate its utility, we present the results of our analyses of two specific problems and compare our results with those obtained by previous investigators.