Radial dependence of adsorption and desorption timescales of HF from various types of grain surfaces. The top half of the figure relates to the envelope of core I(N), the bottom half to that of core I. The small panels above each main panel depict the physical structure (temperature in solid blue, left axis; density in dashed red, right axis) for the envelopes in question from Van der Tak et al. (2013). The horizontal axis is logarithmic cumulative mass increasing from left to right; labels in brackets indicate the percentage of enclosed mass starting from the outer shell of the core. Freeze-out of HF (depletion from the gas phase) occurs in the region where t_desorb>t_freeze; light shading indicates the case of H₂O ice mantles, darker shading that of CO/CO₂ ice mantles. The desorption timescale lines for CO ice and CO₂ ice in the bottom panel lie to the far right, outside of the limits of the axes.