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 1991, with 24 samples collected in a 3-m snowpit covering the previous 4 years of deposition. All concentrations were below detection limits (a few pg kg-1) in the soluble phase, while concentrations of 13 PAHs were determined in the insoluble fraction. These are essentially the same as those which are present in the aerosol at this location. The nature of the PAHs in the ice shows that the contamination is due essentially to fossil fuel combustion aerosols coming from industrial zones, and also to biomass burning aerosols. 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 indicate summer minima for all species, attributed to lower emissions and reactions in the atmosphere at that time of the year. The maxima take place in spring for many compounds, in phase with that of sulfate, and is tentatively attributed to the influence of Arctic Haze. However, concentration increases are already seen in winter, particularly for 3-ring species that peak at that time. This situation could reflect the larger emissions in winter; but indicates also differential scavenging among the compounds and specific transport pathways. Finally, the snowpit 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 atmospheric reactivity index of the compounds. This study shows that PAHs are good geochemical anthropogenic tracers; they can be used to know the composition of the atmosphere since the beginning of the industrial period.