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

Abstract

As a major sink of atmospheric nitrogen oxides (NOx=NO+NO2), nitrate (NO3-) in polar snow can reflect the long-range transport of NOx and related species (e.g., peroxyacetyl nitrate). On the other hand, because NO3- in snow can be photolyzed, potentially producing gas phase NOx locally, NO3- 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 NO3- to determine the degree to which local processes influence atmospheric and snow NO3-. 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, NOy, HNO3, and nitrite (NO-2)) and the NO3- isotopic composition or concentration in snow. This suggests that (1) the snow NO3- at Summit is primarily derived from long-range transport and (2) this NO3- is largely preserved in the snow. Additionally, three isotopically distinct NO3- sources were found to be contributing to the NO3- in the snowat Summit during both 2010 and 2011. Through the complete isotopic composition of NO3-, we suggest that these sources are local anthropogenic particulate NO3- from station activities (δ15N=16‰, Δ17O=4‰, and δ18O=23‰), NO3- formed from midlatitude NOx (δ15N=-10‰, Δ17O=29‰, δ18O=78‰) and a NO3- source that is possibly influenced by or derived from stratospheric ozone NO3- (δ15N=5‰, Δ17O=39‰, δ18O=100‰).