| Abstract
| - The emergence of Cl- ions from the surface of alkali halide salts at low relative humidity (RH) is predictedby density functional theory (DFT) calculations and supported by contact potential measurements. We findfrom DFT that, in the presence of water at the regime of one monolayer coverage on the (100) cleavageplane of NaCl, Cl- ions are displaced at very low energetic cost from their crystal lattice positions toward theplane of water molecules. Starting from plausible low-temperature layered structures, we use total energyDFT to calculate the energy cost to bring Cl- ions to the height of the water layer. We show the importanceof the screening of the electrostatic interactions by the water layer in order to explain our findings and todetermine the value of the surface dipole as a function of the chloride position. The theoretical surface dipoleis used to estimate the concentration of raised Cl- ions at the surface. As dissolved chloride ions are thereactive component of the sea salt aerosols at high RH, we propose that the facile destabilization of Cl- isone of the mechanisms behind the catalytic activity of NaCl at low RH on reactions involving atmosphericgases.
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