We study the transfer of a CO2 molecule from the gas phase through a thin liquid water film supported on ionic single crystal surfaces NaCl and MgO (001). The free energy profile for the CO2 is calculated at 300 K using constrained molecular-dynamics simulation, and the detailed analysis of the competition between interaction and entropic contributions can help to the understanding of the pollution kinetic process of a water covered solid surface. It is shown that the CO2 solvation and its adsorption directly on the solid surface is easier for a NaCl supported film than for a MgO one.