The dispersion produced by a jet injecting microparticles in a cross stream is controlled by the interaction between dispersed species and large-scale time-dependent flow structures populating the transverse jet. These structures span over a wide range of spatial and temporal scales and are not equally effective in advecting and dispersing species. In many environmental and industrial applications, the species advected by the jet stream are expected to undergo rapid and homogeneous dilution away from the injection point. Preferential accumulation of particles into specific flow regions may have consequences on the overall industrial process. For instance, nonuniform particle distribution can severely downgrade the efficiency of postcombustion devices. In this work, we address the problem of identifying which of the flow structures in a jet in crossflow controls dispersion mechanisms of inertial particles, focusing specifically on the issue of their preferential distribution. The flow field produced by the transverse jet is calculated using a finite-volume solver of Navier-Stokes equations and the dispersion of particles is computed using a Lagrangian approach. We investigate the behavior of particles of different sizes, examining 5 orders of magnitude of their inertial parameter-the particle timescale. The analysis of dispersion shows that particle distribution is not uniform and is dominated by specific flow structures. Examining the distribution of the different particles in connection with particle timescale and flow structure evolution, it is found that shear layer vortices initially control dispersion and segregation processes, whereas counter-rotating vortices entrain and trap particles in the lee side of the jet. (D 2004 American Institute of Chemical Engineers.