Top panel: size distribution of particles in the protoplanetary disc at different times during disc evolution for our nominal model. The semimajor axes of the formed planetesimals are indicated at the top of the plot. Particles were initialized with an equal spacing all over the disc and with a radius of 1 μm. Efficient coagulation and high drift velocities in the inner disc result in a depletion of the interplanetary regions after only a few 100 000 yr. These processes occur on a longer timescale in the outer disc. Bottom panel: particle Stokes number versus semimajor axis for the same data as in the top panel.