Time evolution of abundances of methanol in blue and acetaldehyde in red (bottom) and their ratios in purple (top) for the same injected methanol abundance, 3 × 10⁻⁶, and ethyl radical value, 3 × 10⁻⁷. The different line styles correspond to models run with different conditions, as reported in the upper panel legend. The CH₃ OH/CH₃CHO abundance ratio is constant if both species are directly injected from the grain mantles (see text).