Radial profile of the surface densities of the gas and the dust at different time snaps t = 10⁵,3 × 10⁵ and 10⁶   yr. The solid lines correspond to the dust surface density while the gas surface density is shown using the dashed lines. The (red-coloured) dotted line refers to Σ_g ~ R^-1 and Σ_d = Ṁ_d/(2πR ⟨ v_R,d ⟩ ) at t/t_K = 0. |Ṁ_d| = 10^-10   M_⊙/yr, α = 10^-3, and ϱ_p = 1.0   g   cm^-3. The profiles shown in the left panel are obtained under the assumption of spherical grains with a₀ = 1   mm. The corresponding profiles obtained for agglomerates with D_BCCA = 2 and N = 10¹² monomers of a₀ = 10^-5   cm are shown in the right panel.