Since the NaCl and Na 2 SO 4 crusts have different pore size distributions, as indicated by SEM measurements (Fig. ), their respective surface-to-volume ratios and the corresponding relative amount of 'small' pores is expected to be different, which will affect the frequency dependence of T 1 . NaCl and Na 2 SO 4 solid surfaces also have different surface chemistry, SO 2- 4 ions bear a -2e charge, compared to the -1e charge of the Cl -ions. Differences in surface chemistry are likely to impact the water structure, as well as the characteristic residence time of the molecules at the solid walls. In order to obtain results from NaCl and Na 2 SO 4 systems with a controlled surface-to-volume ratio, MD simulations of pure water confined within slit nanopores were performed (results obtained with salt solutions with finite concentration are presented in the next subsection). The surface area of the nanopore was chosen as A ≈ 16 nm 2 , and the distance between the wall was varied from h ≈ 0.4 nm (about one water layer thickness) to h ≈ 7 nm (Fig. ). Although such nanometersized slit pores might not be representative for salt crusts, they allow to systematically study the effect of the liquidsolid interface on the relaxation time T 1 .