Distributions of CO (top row), N₂ (middle row), and H₂O (bottom row) ice as functions of time at a fixed medium density of n(H₂) = 10⁶ cm⁻³. Left, middle, and right panels: results for model M3 using 3, 8, or 10 grain size bins, respectively. The blue solid lines indicate the total ice abundance, while the black crosses indicate the corresponding total abundance in our fiducial M3 model. The red, orange, and green lines represent the breakdown of the total ice abundance in the grain size bins as shown in the top right panel. This breakdown is omitted for the fiducial M3 model for clarity.