1D dust evolution. Left: evolution of the size, s, of grains experiencing growth and erosion only, as they grow and drift inwards from different initial distances, r, from the star. The colour represents the Stokes number. The dashed grey line represents the evolution without erosion, while the green, orange, and red lines represent the evolution with growth and fragmentation, using a fragmentation threshold of 20, 40, and 80 m s⁻¹, respectively. The size of the ejected grains is s_ej = 1 mm, a typical value used by R20 and G20. Right: same as the left panel, but with a pressure maximum that traps dust at 1 au.