BROWN SNOW - A LONG-RANGE TRANSPORT EVENT IN THE CANADIAN ARCTIC

We document the occurrence of a long-range transport event that deposited thousands of tonnes of fine particulates on the District of Keewatin, central Canadian Arctic, approximately 63-degrees N. Air mass trajectories, clay mineral composition, soot particles, and visible organic remains point to Asian sources for the "brown snow" material, probably western China. Semivolatile organic pollutants detected in the brown snow included polycyclic aromatic hydrocarbons (SIGMA-PAH), PCB congeners, and DDT-related compounds (SIGMA-DDT), polychlorinated camphenes (PCCs), as well as the herbicide trifluralin and insecticides methoxychlor, endosulfan, and hexachlorocyclohexane (HCH). SIGMA-PAH, PCB, and PCC concentrations were within the range reported in other studies of Arctic snow but SIGMA-DDT levels were 2-10 times higher than previous reports. High molecular weight PAH may have been associated with soot particles in the brown snow but evidence for Asian sources of the pesticides was not strong because of unknown source signal strengths and possible atmospheric transformations of the compounds. Fluxes of these pollutants were also determined by analyzing sediment cores from two small headwater lakes near the sampling site. The quantities of pollutants deposited in this single event may have comprised a significant fraction (> 10%) of total annual input of SIGMA-PAH and SIGMA-DDT, as determined from lake sedimentation records.