The surface density evolution of the dust population for three different simulations at a local simulation at 3 AU. The gray diagonal lines correspond to the required surface densities for a total number of particles of 1, 10³ and 10⁶ in an annulus of thickness 0.1 AU. In the upper panel, all particles initially have a size of 10^-4 cm, and snapshots are taken between 2 and 10⁶ years. In the middle panel, we have run the same simulation, but after 10 800 years, a small number of 1 cm-particles have artificially been inserted. In the lower panel, the bouncing barrier has been replaced with sticking, allowing the particles to freely coagulate to larger sizes.