Measurements of the chemical composition (Cl-, NO3-, SO42 and H+) of ice core samples from Dye 3, Greenland, show recent increases in the concentration of nitrate and sulfate which can be attributed to anthropogenic sources. These anthropogenic sources have changed not only the magnitude of impurity levels in Greenland snow but also the seasonal pattern of impurity concentration. The observed change in seasonal deposition patterns between preindustrial and industrial times is used to analyze the sources of both natural and anthropogenic impurities in Greenland.