Illustration of dust evolution in the two-sized dust population scheme. Three possible examples of dust size distribution at the current time step (blue lines, ) and the next time step (green lines, ) are illustrated. Left: continuous distribution remain continuous during dust growth; center: discontinuous distribution with an excess of small dust turns into a continuous one; right: discontinuous distribution with an excess of grown dust turns into a continuous one. The change in small dust surface density ΔΣ_d,sm is shaded with grey, while added and removed grown dust is shaded by green and blue colors, respectively.