The reaction of NO{sub 2} with NaCl(100) single crystals

Heterogeneous reactions in tropospheric salt aerosols have an important role in atmospheric chemistry. An example of this chemistry, studied in the laboratory, is the reaction of gaseous NO{sub 2} with NaCl crystallites to form solid NaNO{sub 3} and gas phase NOCl. However the surface morphology of these crystallites was not defined, nor was the role of adsorbed water specified. We have chosen to explore the reaction of NO{sub 2} with the NaCl(100) faces of single crystals because their surfaces are well defined and almost defect free. Formation of NO{sub 3}{sup -} and NOCl was monitored as the reaction progressed using infrared spectroscopy. The concentration of NO{sub 3}{sup -} was quantified from the photometry. Up to fifty layers of NaNO{sub 3} are generated on the NaCl substrate before the reaction stops. To better mimic tropospheric conditions, NaCl(100) crystals were exposed to NO{sub 2} with water vapor at low relative humidity. The results from this experiment indicate that the rate of NO{sub 3}{sup -} production is increased a hundred fold. A qualitative picture describing the mechanism of NO{sub 3}{sup -} growth, under these different conditions, will be presented.