Henry's law constants for α-, β-, and γ-hexachlorocyclohexanes (HCHs) as a function of temperature and revised estimates of gas exchange in Arctic regions

Henry's law constants (H. Pam(3)mol (1)) were determined for alpha-, beta-, and gamma-HCH in deionized water over a temperature range of 5-35degreesC using bubble stripping (BS) and dynamic head space (DHS) techniques. The BS method was improved from previous work in the same laboratory by adjusting for loss of water from the stripping chamber over the experiment. This correction resulted in H values that were similar to 15% lower than those calculated without volume adjustments. Good agreement between the BS and DHS methods was found for alpha- and gamma-HCHs, with an average ratio of BS/DHS values=0.99. H values at 20degreesC for alpha- and gamma-HCH were 86-89% of those determined by Jantunen and Bidleman (Chemosphere. Global Change Science 2 (2000) 225), but only 62-69% of the results reported by Kucklick et al. (Marine Chem. 34 (1991) 197). The BS rate of beta-HCH as much slower than for the other HCHs and its H was determined only by the DHS method. Enthalpies of water-to-air transfer, DeltaH(wa). were 59.3 +/-1 1.6, 65.1 +/- 1.3 and 61.4 +/- 3.1 kJ mol(-1) for -, beta- and gamma-HCH, respectively. A reassessment of air-water gas exchange in the western Arctic Ocean and its regional seas was made. based on measurements in 1992-1994. alpha-HCH was significantly (p<0.05) oversaturated (net volatilization) in the south Bering Sea and Beaufort Sea but not significantly different from air-water equilibrium in the Chukchi Sea nor the northern Canada Basin. gamma-HCH was significantly undersaturated (net deposition) in all four regions. This differs from previous estimates which indicated oversaturation of alpha-HCH in the four seas and air-water equilibriurn for gamma-HCH. beta-HCH was oversaturated in the south Bering Sea, undersaturated in the Beaufort Sea and near equilibrium in the Chukchi Sea and northern Canada Basin, Highly accurate H values are required when estimating gas exchange in aquatic systems that are close to air-water equilibrium. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.