Solvation of HCl at <100 K at the surface of nanoparticles of methanethiol, a sulfur derivative of methanol, was investigated by FTIR spectroscopy and on-the-fly molecular dynamics as implemented in the density functional code QUICKSTEP (which is part of the CP2K package). Some of the results have been further checked with MP2-level ab initio calculations. Unlike the HCl-CH3OH system that has been examined before, HCl on the surface or within methanethiol nanoparticles does not achieve an ionized form. Requirements for acid solvation/ionization are discussed in context with the results for methanol clusters. Published under license by AIP Publishing.