Deposition of Aerosols in Polar Regions-Contamination of the Ice Sheet by Polycyclic Aromatic Hydrocarbons

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Abstract
As part of the GRIP-GISP programme, sampling of superficial polar ice was carried out in the neve of the Summit station situated in the centre of Greenland, during summer 1991. Twenty-four samples were taken from the first three meters of the ice layer. This is a record of the organic matter concentrations of the air during last five years. This first study concerns the polycyclic aromatic hydrocarbons (PAH) present in the insoluble phase of the ice. It shows that, in the atmosphere, PAH adsorbed on fine particles travel over long distances from industrial regions, especially from Russia and East Europe or, may be, from low latitudes regions to polar regions. Then they are deposited during snow falls and are archived in the ice. All the PAH emitted by fossil fuel combustion are present in the insoluble phase of the ice. However PAH produced by biomass combustion are also present in the ice in essar abundance. On average the total amount of PAH is of the order of a few hundred picogramms per kg of ice (1360 pg.kg-1). the PAH concentration profile is little different from that of PAH present in aerosols collected at the same station during summer. the transfer from air to snow and snow to compacted ice occurs without important physicochemical transformation. Nevertheless, the relatively low concentration of reactive compounds like Benzo [a] Pyrene shows that the reactivity in the ice is not negligible, but we do not know if the mechanisms involved in this process are the same in the ice and in the atmosphere. The variation of the total concentrations shows a seasonal dependance over the 5 years with a first maximum towards the spring corresponding to strong tropospheric contribution of medium latitude, a second maximum in winter corresponding to strong emissions in industrial regions and a minimum in summer, a period where the degradation during transport by reaction of PAH with OH radicals is important. This set of data can be used to evaluate the global contamination by PAH.