BERYLLIUM-7 AND PB-210 IN AEROSOL AND SNOW IN THE DYE-3 GAS, AEROSOL AND SNOW SAMPLING PROGRAM

Concentrations of cosmogenic Be-7 and the radon daughter Pb-210 were d etermined in surface-level aerosols and fresh and aging snow throughou t DGASP. The distinct sources, yet common association with submicron a erosols, of these atmospheric radionuclides makes them valuable tracer s of the transport, depositional and post-depositional processes leadi ng to incorporation of submicron aerosols (and associated species) int o the Greenland Ice Sheet. The aerosol concentrations of atmospheric r adionuclides tended to covary on the 1-7 day time scale of individual samples (r=0.57, n=114, p=0.001) and were also highly correlated when averaged by month (r=0.80, p=0.002). The year-long time series of both Be-7 and Pb-210 showed concentration peaks in spring (April) and fall (September-October) and minima in summer (July) and winter (November- February), This finding is in stark contrast to results from other arc tic sites, where both radionuclides, but particularly Pb-210, show pro nounced concentration peaks in the winter. This indicates that the air masses over the Greenland Ice Sheet may be distinct from the air in t he polar basin, or boundary layer processes strongly bias surface-leve l aerosol characteristics over the ice sheet, or, likely, some combina tion of these factors are operating. The concentrations of Be-7 and Pb -210 in fresh snow at Dye 3 show wide variability between snow fall ev ents. The lack of any obvious correlation between concentrations in ae rosol and fresh snow support the contention that surface-level air at this site is often not reflecting air aloft. Aging snow studies did no t reveal consistent trends in concentration, suggesting important hete rogeneity in the initial concentrations of Be-7 and Pb-210 in surface snow over small spatial scales. Poor agreement between the Pb-210 prof ile in a 2 m snowpit sampled at the end of the project and the observe d deposition of Pb-210 through the year indicate the potential importa nce of post-depositional processes in modifying the atmospheric ''sign als'' preserved in the snowpack.