POLYCYCLIC AROMATIC-HYDROCARBONS IN THE POLAR ICE OF GREENLAND - GEOCHEMICAL USE OF THESE ATMOSPHERIC TRACERS

Sampling of surface snow for PAH analysis took place at the Summit of the Greenland Ice Sheet in summer 1998, with 24 samples collected in a 3-m snowpit covering the previous 4 years of deposition. All concentr ations were below detection limits (a few pg kg-1) in the soluble phas e, while concentrations of 13 PAHs were determined in the insoluble fr action. These are essentially the same as those which are present in t he aerosol at this location. The nature of the PAHs in the ice shows t hat the contamination is due essentially to fossil fuel combustion aer osols coming from industrial zones, and also to biomass burning aeroso ls. The total amount of PAH is on the order of a few hundred pg kg-1 ( 1360 pg kg-1) on average. The concentration profiles in the ice indica te summer minima for all species, attributed to lower emissions and re actions in the atmosphere at that time of the year. The maxima take pl ace in spring for many compounds, in phase with that of sulfate, and i s tentatively attributed to the influence of Arctic Haze. However, con centration increases are already seen in winter, particularly for 3-ri ng species that peak at that time. This situation could reflect the la rger emissions in winter; but indicates also differential scavenging a mong the compounds and specific transport pathways. Finally, the snowp it profile shows that some modification occurs after deposition, with for example a 90% decrease of benzopyrene concentrations in the course of 4 years. The rate of change seems in rough agreement with the atmo spheric reactivity index of the compounds. This study shows that PAHs are good geochemical anthropogenic tracers; they can be used to know t he composition of the atmosphere since the beginning of the industrial period.