To test the recent advances in receptor modeling for the identification of long-range transport of regional source signatures of airborne particulate matter, an epithermal irradiation facility to determine indium has been specifically constructed. Analysis of filter samples collected weekly over a 5-yr period has indicated that indium in the arctic atmosphere is strongly dependent on season. Typical detection limits were 0.1 ng per one-eighth of a 20.3- × 25.4-cm Whatman filter. The airborne concentrations of indium are extremely elevated in the winter and spring months, and they almost disappear in the summer months. The application of the potential source contribution function has indicated that the indium originates from several areas in Eurasia as well as from known “hot spots” in North America.