Particle density distribution after 1 Myr of evolution as a function of distance from the star and grain size of the models without any pressure bump (Table 1). The solid white line represents a Stokes number of unity. Cyan and red show the fragmentation (Eq. (A.17)) and drift (Eq. (A.32)) limit. The style of the line shows what dominates the relative velocity: turbulence (Eqs. (A.16) and (A.27)), radial drift (Eqs. (A.10), and (A.24)), and settling (Eqs. (A.15) and (A.25)). We do not include the turbulence I regime or the azimuthal drift because they do not dominate the relative velocities in any case for the shown snapshot. The horizontal gray line shows a = 1 mm, and we call pebbles all particles that are larger than this.