Data are provided for a pure ethanol sample (experiment A) as well as an ethanol:CO mixture (experiment D) to illustrate the importance of acetaldehyde as a driver of chemistry in our photolysis experiments. (a) The fractional composition of the sample, over the course of irradiation, as determined from the column densities. Only species with appreciable contributions are shown for clarity. (b) The partitioning of the photon absorption events among the various ice components, as defined in Eq. (8). (c) The probability that an arbitrary molecule in the sample will have the indicated molecule as one of its nearest-neighbors; see Appendix C.