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tokens: lines is explained by (i) the very similar upper level energy and critical densities ( E up = 33 K, and 35 K, and n cr ∼ 7−5 × 10 5 cm −3 , and 17−9.5 × 10 5 cm −3 , at 20−100 K, for the H 2 CO and the CS line, respectively, Shirley 2015 ) and (ii) the similar distribution of the H 2 CO and CS abundance in the disk suggested by thermo-chemical models (e.g., Fedele Favre 2020 ). Both molecules are released from grains and/or formed in the gas phase in the molecular layer, following the photodissociation of CO, which makes available C for the formation of small hydrocarbons, together with atomic O. The CS is formed from reactions of small hydrocarbons with either ionized or atomic S (e.g., Le Gal et al. 2019 ), while the main formation route of H 2 CO is via the reaction CH 3 +O (e.g., Loomis et al. 2015 ). Additionally, CO 2−1 and CS 5−4 emissions strongly decrease in the outer disk-midplane, where molecules freeze-out onto dust grains (freeze-out layer). By contrast, H 2 CO is only a factor of 2 less intense, which indicates that the H 2 CO molecules trapped on the icy grains in the cold midplane are partially released by nonthermal processes (UV, X-ray, cosmic-rays-induced, and/or reactive desorption). We tentatively detected CH 3 OH emission at 3 σ in the disk region where H 2 CO and CS emissions are bright, that is to say the warm molecular layer where molecules should be efficiently released from grains, while it remains undetected in the outer disk midplane. In the right panel of Fig. 3 , the [CH 3 OH]/[H 2 CO] abundance ratio inferred for the Class I disk of IRAS 04302 is compared with the estimates obtained in hot corinos around Class 0 protostars, in the other Class I disks observed by ALMA-DOT, in the Class II disks of TW Hya and HD 163296, and in comets. The abundance ratio in the disk of IRAS 04302 (∼0.5−0.6 for T ex ∼ 20−100 K) is consistent with the upper limits derived for the other Class I and early Class II disks observed by ALMA-DOT (between 0.7 and 3.2, Podio et al. 2019 ; Garufi et al. 2020 , and in prep.). On the other hand, it is lower by a factor of ∼2.5 than that inferred for the Class II disk of TW Hya (∼1.27−1.73 for T ex ∼ 25−75 K, Walsh et al. 2016 ; Carney et al. 2019 ), while it is larger than the upper limit obtained for HD 163296 ( 0.24, Carney et al. 2019 ). As methanol forms on the dust grains due to CO freeze-out and subsequent hydrogenation, the lower [CH 3 OH]/[H 2 CO] in HD 163296 may be due to a smaller degree of CO ice chemistry in the warmer disks around Herbig stars (e.g., Pegues et al. 2020 ). The abundance ratios in Class I and Class II disks are from a factor of 2 to 2 orders of magnitude lower than the values inferred in the hot corinos around the Class 0 protostars IRAS 16293-2422 A and B in Taurus ( Jørgensen et al. 2018 ; Persson et al. 2018 ; Manigand et al. 2020 ), and NGC 1333-IRAS 4A and IRAS 2A in Perseus ( Taquet et al. 2015 ). This difference may be due to an evolution of the methanol and