Trajectory analysis of source regions influencing the south Greenland Ice Sheet during the Dye 3 Gas and Aerosol Sampling Program

Backward air mass trajectories for Dye 3, Greenland (elevation 2.5 km) show source regions that vary with season: the direction of greatest transport distance is from the southwest in fall, west in winter, and northwest in spring; the trajectories in summer do not show a strong preferred direction. Based on 5 d transit times, the trajectories in fall suggest the importance of North America as a potential source region, with occasional trajectories from western Europe. The trajectories in spring, especially in April, suggest Eurasia (transport over the Pole), eastern North America, and Western Europe as potential source regions. Less transport of chemical constituents to Dye 3 is expected in summer when transport distances are shorter. Although some long-range transport to Greenland occurs in winter, the stability of the atmosphere over the ice sheet at this time of year is likely to limit the delivery of chemical constituents to the surface. Sources outside of these regions can also influence Dye 3 if transit times longer than 5 d are considered. These results are in contrast to trajectories reported by others for sea-level arctic locations such as Barrow, Alaska and Mould Bay, Canada, where transport over the Pole from Eurasia is responsible for high chemical species concentrations over much of the winter and early spring. Overall, the trajectories are consistent with aerosol chemical data for this time period at Dye 3 reported by several investigators, showing peak concentrations in spring and fall.