A common phenomenon in deposition processes is the impaction of a particle on a pre-deposited panicle in a deposit (e.g.. as in thin film growth via aerosol routes or in gas-side fouling of heat exchange equipment). The fate of an incident panicle (i.e., whether it sticks on the deposit or it escapes) affects the net deposition rate. as well as the resulting deposit microstructure, phenomena that we have been studying, using discrete particle computer simulations. Here, we summarize the sticking behavior of impacting particles in terms of appropriate macroscopic "boundary conditions" that can be used in continuum level simulations of the dynamics of deposit growth. In addition. we study the properties of rebounding/scattered particles from a "rough" particulate deposit surface, in terms of rebounding linear and angular velocities and scattering angle distributions. Interestingly enough, the rebounding velocity distributions exhibit a multimodal character which becomes less pronounced with the degree of "rigidity" of the deposit, reflecting the influence of local microstructural details (coordination number distribution) on the scattering process. Scattering angle distributions are unimodal, resembling a "distorted" sinusoidal. The remaining challenge is to develop, with further parametric studies, appropriate "boundary conditions" for the scattering quantities of interest as well, and open the door to continuum level simulations of macroscopic systems in realistic geometries.