Fractional abundance of methanol gas as a function of z∕r for radii of 10 (left), 20 (middle), and 30 (right) au. Results are shown for three different non-thermal desorption mechanism: photodesorption only (top), reactive desorption only (middle), and codesorption with CO only (bottom). The colour gradient from light to dark represents four different time steps: 0.5, 1.0, 5.0, and 10 Myr. The grey lines in the top and middle plots represent the “fiducial” model as described in the text (i.e. photodesorption of intact methanol with a yield of ~10⁻³ and a reactive desorption probability of 1%). The vertical grey lines in the plots at 20 and 30 au mark the CO snow surface (see Fig. 8). The horizontal bar indicates the methanol abundance as observed towards TW Hya by Walsh et al. (2016).