Abundances of gas-phase H₂CO (top panels) and CH₃OH (bottom panels) with respect to H₂ as a function of the time in simulations M_TD (solid lines), M_10 (dashed lines), and M_0 (dotted lines). From left to right, the columns show the evolution in a cell that starts at r ~ 200 au, r ~ 1 × 10⁴ au, or r ~ 2 × 10⁴ au. The noise in the CH₃OH abundances in the innermost cell reflects the temperature fluctuations (Fig. 1), which affect the abundance of hydrogen on the grain surface (gas-phase CH₃OH is mostly coming from chemical desorption of methanol formed by the CH₃O + H reaction on the grains).