Vertically integrated dust density distribution at 1 Myr for A = 0.1 and f = 1 (top) and A = 0.1 and f = 3 (bottom). The white line shows the particle size corresponding to a Stokes number of unity, which shows the same shape as the gas surface density Σ′ of Eq. (1) (see Eq. (8)). The blue line represents the maximum size of the particles before they reach fragmentation velocities (fragmentation barrier according to Eq. (15)).