The collision frequency map for the scenario where 1 cm-particles are artificially inserted at t = 10   800 years. The interaction frequency is plotted for each particle pair at six different timesteps plotted on top of the collision outcome space of Fig. 8. This makes it possible to identify the dominating interaction for each particle size. Note the persistently high peak of interactions with particles stuck below the bouncing barrier at 1 mm in size. As the large particles grow, they also sometimes collide among themselves, producing a tail of particles capable of also sweeping up the bouncing particles. This causes an increase in both mass and number for the large particles, and a continuous widening of the size-distribution.