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We present boreal forest fire proxies in a northwest Greenland snowpit spanning a period of six years, from spring 2003 to summer 2009. Levoglucosan (C 6 H 10 O 5) is a specific organic molecular marker of biomass burning caused by boreal forest fires. In this study, levoglucosan was determined via liquid chromatography/negative ion electrospray ionization-tandem mass spectrometry, wherein isotope-dilution and multiple reaction monitoring methods are employed. Ammonium (NH 4 +) and oxalate (C 2 O 4 2−), traditional biomass burning proxies, were determined using two-channel ion chromatography. In the northwest Greenland snowpit, peaks in levoglucosan, ammonium, and oxalate were observed in snow layers corresponding to the summer–fall seasons of 2004 and 2005. Considered together, these spikes are a marker for large boreal forest fires. The levoglucosan deposited in the Greenland snow was strongly dependent on long-range atmospheric transportation. A 10-day backward air mass trajectory analysis supports that the major contributors were air masses from North America. In addition, satellite-derived carbon monoxide (CO) and ammonia (NH 3) concentrations suggest that chemicals from North American boreal forest fires during the summer–fall of 2004 and 2005 were transported to Greenland. However, large boreal fires in Siberia in 2003 and 2008 were not recorded in the snowpit. The sub-annual resolution measurements of levoglucosan and ammonium can distinguish between the contributions of past boreal forest fires and soil emissions from anthropogenic activity to Greenland snow and ice. [Display omitted] • North American boreal fires in 2004 and 2005 are imprinted in Greenland snow. • Peaks of Levoglucosan in Greenland snow reflect large boreal fires. • Levoglucosan coincides with ammonium and oxalate in Greenland snow. • Trajectory analysis and satellite-based CO support a North America source. [ABSTRACT FROM AUTHOR]