Snapshots taken from the RAMSES MHD models (ℳ₀ and ℳ₁) of a collapsing protostellar envelope (initial parameters can be found in the text) with dust grain size evolution computed by COALA. The maps show a 2000 au zoom in on the model when the central star has accreted 0.4 M_⊙from the initial 2.5 M_⊙core. The red cross represents the position of the star. The left column shows the total column gas density, Σ. The middle column shows the average grain size at the peak of the size distribution, a_peak, weighted by the gas density along the line of sight (see the main text for further details). Similarly, the right column shows the average dust enrichment (ratio between the evolved dust-to-gas ratio, ϵ, and the initial dust-to-gas ratio, ϵ₀) weighted by the gas density along the line of sight. In the top row, the square patterns near the sink are not numerical artifacts but result from the weighted average of the quantities along the line of sight.