Chemical-mechanical polishing (CMP) involves complex mechanical and chemical interactions between a rough elastomeric pad, the wafer being polished and an abrasive slurry containing sub-micron diameter silica particles. The interaction between these abrasive particles and the wafer surface and their impact upon material removal rates is still unclear. Particle dynamics in a model CMP geometry are studied experimentally in this work. Only the particles that actually interact with, and presumably polish, the model wafer surface are visualized using total internal reflection fluorescence (TIRF). The effect of process properties such as particle diameter, particle material, pad-wafer separation and shear rate upon the particle concentration immediately adjacent to the wafer surface is investigated.