Results obtained assuming that GA forms in the gas phase via the ethanol tree and is injected from the grain mantles into the gas phase at the passage of the shocks. The injected ethanol is 3 × 10⁻⁸ in the left panels and 15 × 10⁻⁸ in the right panels. Model predictions (curves) are compared with the observations (symbols) toward B0, B1 and B2, assuming three different excitation temperatures T_ex = 15 K (crosses), 30 K (triangles) and 50 K (squares). In each figure, the upper panels show the abundances of GA (blue) and ethanol (red) as a function of time. The bottom panels show the evolution with time of the GA/ethanol abundance ratio.