A systematic analysis of the impacts of heat patches and topographical features on the dispersion of passive materials in a shear-free convective boundary layer (CBL) was performed. A coupled large-eddy simulation (LES) and Lagrangian particle dispersion (LPD) model was used for that purpose. Over a homogeneous, flat terrain the dispersion statistics produced by the model is in excellent agreement with convection tank data and with other model results. Heat flux heterogeneity has a remarkable influence on particle dispersion in the CBL. The horizontal pressure gradients created by these heterogeneities impede vertical mixing. For a near surface
release, the particles travel horizontally rather than "lifting-off," increasing the concentration near the ground surface. Particles released at higher elevations reach the surface much slowly than when released above a flat, homogeneous domain. Topography has very little impact on "lift-off," dimensionless crosswind integrated concentration, mean particle height, particle spread and ground level concentration of particles released near the ground surface. This is true even
with hills as high as 25% the height of the CBL. However, it has a noticeable effect on the dispersion statistics of particles released from higher elevations. In particular, for a source height located about 1/4 the height of the CBL, the locus of the maximum concentration in cross-wind
integrated plume descends to the surface of a moderate hill noticeably slowly than above a flat, homogeneous domain.