Analysis of nitrate in the snow and atmosphere at Summit, Greenland: Chemistry and transport

As a major sink of atmospheric nitrogen oxides (NO x  = NO + NO 2 ), nitrate (NO 3 − ) in polar snow can reflect the long‐range transport of NO x and related species (e.g., peroxyacetyl nitrate). On the other hand, because NO 3 − in snow can be photolyzed, potentially producing gas phase NO x locally, NO 3 − in snow (and thus, ice) may reflect local processes. Here we investigate the relationship between local atmospheric composition at Summit, Greenland (72°35′N, 38°25′W) and the isotopic composition of NO 3 − to determine the degree to which local processes influence atmospheric and snow NO 3 − . Based on snow and atmospheric observations during May–June 2010 and 2011, we find no connection between the local atmospheric concentrations of a suite of gases (BrO, NO, NO y , HNO 3 , and nitrite (NO 2 − )) and the NO 3 − isotopic composition or concentration in snow. This suggests that (1) the snow NO 3 − at Summit is primarily derived from long‐range transport and (2) this NO 3 − is largely preserved in the snow. Additionally, three isotopically distinct NO 3 − sources were found to be contributing to the NO 3 − in the snow at Summit during both 2010 and 2011. Through the complete isotopic composition of NO 3 − , we suggest that these sources are local anthropogenic particulate NO 3 − from station activities (δ 15 N = 16‰, Δ 17 O = 4‰, and δ 18 O = 23‰), NO 3 − formed from midlatitude NO x (δ 15 N = −10‰, Δ 17 O = 29‰, δ 18 O = 78‰) and a NO 3 − source that is possibly influenced by or derived from stratospheric ozone NO 3 − (δ 15 N = 5‰, Δ 17 O = 39‰, δ 18 O = 100‰).