Title Different photolysis kinetics at the surface of frozen freshwater vs. frozen salt solutions
Author Kahan, T.F.; Kwamena, N.O.A.; Donaldson, D.J.
Author Affil Kahan, T.F., University of Toronto, Department of Chemistry, Toronto, ON, Canada
Source Atmospheric Chemistry and Physics, 10(22), p.10917-10922, . Publisher: Copernicus, Katlenburg-Lindau, International. ISSN: 1680-7316
Publication Date 2010
Notes In English. Published in Atmospheric Chemistry and Physics Discussions: 7 May 2010, http://www.atmos-chem-phys- discuss.net/10/12063/2010/acpd-10-12063-2010. html; accessed in May, 2011. 28 refs. GeoRef Acc. No: 310360
Index Terms brines; ice; liquid phases; photochemical reactions; physical properties; pollution; snow; solid phases; solutions; spectra; surface waters; aqueous solutions; atmosphere; chemical reactions; fluorescence; fresh water; harmine; kinetics; liquid phase; organic compounds; partitioning; phase equilibria; photochemistry; photolysis; pollutants; Raman spectra; rates; salt water; sea ice; sodium bromide; sodium chloride; sodium halide; solid phase; surface water
Abstract Reactions at air-ice interfaces can proceed at very different rates than those in aqueous solution, due to the unique disordered region at the ice surface known as the quasi-liquid layer (QLL). The physical and chemical nature of the surfacial region of ice is greatly affected by solutes such as sodium halide salts. In this work, we studied the effects of sodium chloride and sodium bromide on the photolysis kinetics of harmine, an aromatic organic compound, in aqueous solution and at the surface of frozen salt solutions above the eutectic temperature. In common with other aromatic organic compounds we have studied, harmine photolysis is much faster on ice surfaces than in aqueous solution, but the presence of NaCl or NaBr--which does not affect photolysis kinetics in solution--reduces the photolysis rate on ice. The rate decreases monotonically with increasing salt concentration; at the concentrations found in seawater, harmine photolysis at the surface of frozen salt solutions proceeds at the same rate as in aqueous solution. These results suggest that the brine excluded to the surfaces of frozen salt solutions is a true aqueous solution, and so it may be possible to use aqueous-phase kinetics to predict photolysis rates at sea ice surfaces. This is in marked contrast to the result at the surface of frozen freshwater samples, where reaction kinetics are often not well- described by aqueous-phase processes.
URL http://www.atmos-chem-phys.net/10/10917/2010/acp-10-10917-2010.pdf
Publication Type journal article
Record ID 65007211