Modeling interfacial properties is a major challenge for mesoscopic simulation methods. Many-body dissipative particle dynamics (MDPD) is then a promising method to model heterogeneous systems at long time and length scales. However no rule exists to obtain a set of MDPD parameters capable to reproduce the thermodynamic properties of a molecular system of a specific chemistry. In this letter, we provide a general multiscale method to obtain a set of parameters from atomistic simulations using Flory−Huggins theory (FH) to be used with dissipative particle dynamics. We demonstrate the high quality and the transferability of the resulting parameters on the salt concentration dependence of surface tension. We also show the specificity of inorganic salt at the water−air interface. Our results indicate that the increase of surface tension with the salt concentration cannot be explained in terms of the charge image concept based on the Wagner, Onsager, and Samaras theory but rather in terms of the ion hydration.