Size distributions that qualitatively reproduce the expected size evolution behaviour for dust grain growth in aggregation models. The lower bound of the grain sizes is kept constant at 0.005 The upper bound of the distribution is varied from 0.25 µm (MRN distribution) to 1 µm (τ₁), 3 µm (τ₃) and 5 µm (τ₅), and the slope is defined to maintain the same total mass. See text for details.