The concentrations of 7Be and 210Pb were measured in surface air and fresh and aging snow samples from Summit (72¿20'N, 38¿45'W) and Dye 3 (65¿10'N, 44¿45'W) Greenland, during June and July 1989. The aerosol concentrations of these radionuclides showed rapid variations at both sites, but were nearly twice as high, on average, at Summit. Concentrations in the 16 fresh snowfall events that were sampled also showed wide variability, but the averages were the same at the two sites. The apparent difference in air-snow fractionation adn the lack of coeherence in the concentration in air time series between the two sites indicate previously unsuspected complexity in atmospheric dynamics over the ice sheet. Improved understanding of atmospheric processes, and how the results of those processes are recorded in snow and ice, is crucial for full interpretation of the information about past atmospheric chemistry and climate contained in the snow and ice of glaciers around the world. ¿ American Geophysical Union 1990