| Abstract
| - Adsorbed water has been shown to enhance the ionic mobility on NaCl surfaces at water vapor pressureswell below the deliquescence point. This has important implications for the steady-state reactivity of NaCl,in atmospheric sea salt particles, with nitrogen oxides in the atmosphere. In the absence of surface ionicmobility the surface passivates due to the buildup of a product layer. It has also been suggested that theactual reaction probability of the reaction of HNO3 with NaCl surfaces may depend on the water content ofthe surface. Using X-ray photoelectron spectroscopy and electron microscopy, we show that the specifics(particle size and water exposure) of the NaCl sample preparation can have significant effect on the amountof strongly adsorbed water (SAW) on the surface. Specifically, large single crystals of NaCl(100) do notadsorb water strongly. Crystallites in the size range of 500 μm adsorb small amounts of water strongly. Incomparison, small crystallites in the size range of 1−10 μm can adsorb large amounts of water strongly. Thestrongly adsorbed water remains on the surface when exposed to vacuum at temperatures above 100 °C. TheNaCl small crystallites, with the largest amount of strongly adsorbed water, do show a small increase in theinitial reaction probability for the reaction with HNO3. This increase in initial reaction probability is at mosta factor of 4. By combining the results presented here with our previously reported quantitative measurementof the reaction probability for HNO3 on NaCl(100) single-crystal surfaces we recommend a value of γ = (5.2± 3) × 10-3 for the reaction probability of gaseous HNO3 with micrometer-size NaCl particles that containstrongly adsorbed surface water.
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