Hexachlorocyclohexanes (HCHs) in the Canadian archipelago. 2. Air-water gas exchange of alpha- and gamma-HCH

Air and water were sampled in the Canadian Archipelago during summer on the Tundra Northwest 1999 (TNW-99) expedition and air was sampled at Resolute Bay (1313), Nunavut, to determine the gas exchange of a-and gamma-hexachlorocyclohexanes (HCHs) and the enantiomers of alpha-HCH. Air concentrations of Sigma HCH during TNW-99 and at RB were similar, averaging 55 and. 53 pg m(-3), respectively. The net gas exchange direction was volatilization for alpha-HCH and near equilibrium or deposition for gamma-HCH, whereas actual fluxes depended on the fraction of open water. Enantiomer fractions, EF = (+)/[(+) + (-)] of alpha-HCH in air sampled from shipboard were significantly correlated to those in surface water for events with >90% open water, but were closer to racemic and not correlated to EFs in water for events with 0-50% open water. Levels of alpha-HCH in air at RB averaged 37 9 pg m(-3) from June to early July, and EFs were close to racemic (0.496 +/- 0.004). In mid-July the ice pack broke up around RB. From this point through August, air concentrations increased significantly to 53 +/- 5 pg m(-3), and the mean EF decreased significantly to 0.483 +/- 0.009. Air concentrations of gamma-HCH at RB did not differ significantly before (8.0 +/- 3.7 pg m(-3)) and after (6.6 +/- 0.76 pg m(-3)) ice breakup. Results show that a-HCH enantiomers are sensitive tracers for following the impact of ice cover loss on gas exchange in the Arctic.