The Dye 3 gas and aerosol sampling program (DGASP): An overview

DGASP was designed as an international effort to study the processes influencing chemical species that eventually reach the deep ice in the south of Greenland. These processes include long-range atmospheric transport, wet and dry deposition to the snow surface, and changes during aging of the snow. The program took place during August 1988-July 1989. Experimental work included sampling of aerosols and gases, collection of fresh and older surface snow, and sampling of snowpits. The various samples were analysed for chemical species that are tracers of specific sources categories. Results of the program show that the southern Greenland Ice Sheet experiences very different airborne concentration patterns than sea-level arctic sites. Concentrations of SO₄^2-, trace metals, and other species are episodic and peak in April, unlike the consistently high concentrations during January-April seen at lower elevations. Source regions influencing Dye 3 are variable, and include North America, western Europe, and the Arctic Basin. The last region is particularly important, as it may contain relatively high concentrations of chemical constituents from eastern Europe and western Asia that eventually reach Dye 3. The seasonal variations in airborne concentrations are generally also reflected in fresh snow. Similarly, these patterns are seen in snowpits, although some modifications to the glacial record are apparent. Other information on the extent of riming, aerosol/gas partitioning, and aerosol size distributions demonstrate the complexity of air-snow transfer processes, and illustrate the need for further research.