Glycolaldehyde (GA) column density and abundance ratio, computed from the 10_1,10−9_0,9 line, which is the brightest, assuming LTE population and optically thin line emission. The bands represent the uncertainty associated with the line intensity (see text). Upper panel: column density of GA in B0 (light pink), B1 (pink) and B2 (dark pink), as a function of the excitation temperature T_ex. The column density values partially overlap in B0 and B1. Lower panel: GA/ethanol abundance ratio versus T_exc in B0, B1 and B2 (same color coding as above).