An isotopic view on the connection between photolytic emissions of NO_x from the Arctic snowpack and its oxidation by reactive halogens

Abstract

We report on dual isotopic analyses (δ15N and Δ17O) of atmospheric nitrate at daily time‐resolution during the OASIS intensive field campaign at Barrow, Alaska, in March–April 2009. Such measurements allow for the examination of the coupling between snowpack emissions of nitrogen oxides (NOx = NO + NO2) and their involvement in reactive halogen‐mediated chemical reactions in the Arctic atmosphere. The measurements reveal that during the spring, lowδ15N values in atmospheric nitrate, indicative of snowpack emissions of NOx, are almost systematically associated with local oxidation of NOx by reactive halogens such as BrO, as indicated by 17O‐excess measurements (Δ17O). The high time‐resolution data from the intensive field campaign were complemented by weekly aerosol sampling between April 2009 and February 2010. The dual isotopic composition of nitrate (δ15N and Δ17O) obtained throughout this nearly full seasonal cycle is presented and compared to other seasonal‐scale measurements carried out in the Arctic and in non‐polar locations. In particular, the data allow for the investigation of the seasonal variations of reactive halogen chemistry and photochemical snowpack NOx emissions in the Arctic. In addition to the well characterized peak of snowpack NOx emissions during springtime in the Arctic (April to May), the data reveal that photochemical NOx emissions from the snowpack may also occur in other seasons as long as snow is present and there is sufficient UV radiation reaching the Earth's surface.

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer

“…We observed no common trend between δ 15 N and NO x concentrations. Also, no correlation was found between Δ 17 O and δ 15 N, dismissing a common process for these two isotope markers, in contrast to observations made in the Arctic (26). Therefore, δ 15 N was apparently not controlled by the termination reactions leading to the production of nitrate from NO 2 .…”

“…1 shows a seasonal (19,(24)(25)(26), preventing any general hemispheric scale interpretations. We observed no common trend between δ 15 N and NO x concentrations.…”

Spatial variations in snowpack chemistry, isotopic composition of NO<sub>3</sub><sup>−</sup> and nitrogen deposition from the ice sheet margin to the coast of western Greenland

“…Hence, while differential source regions cannot be ruled out, the study areas are very close to each other relative to distances from source regions. A striking result is the similarity of the coastal isotopic data (both δ( 15 N) and ( 17 O) in seasonal snowpack but also in the summer rain samples) with studies much further afield including snowpack at Summit on the ice sheet and atmospheric NO − 3 at Alert, Canada and Barrow, Alaska (Hastings et al, 2004;Kunasek et al, 2008;Morin et al, 2012;. Hence it seems unlikely that differences in source region are a plausible explanation for the spatial differences in the isotopic signatures of snowpack observed in our study.…”

Nitrate stable isotopes and major ions in snow and ice samples from four Svalbard sites

“…1). These new data help to better define the spatial and temporal variability of NO À 3 isotopic signatures across Svalbard by complementing previous measurements from the atmosphere and snow made near Ny-Å lesund (Heaton et al 2004;Morin et al 2009;Morin et al 2012;. We also present back-trajectory analyses of air masses associated with precipitation events at the different sampling sites to help identify NO À 3 source regions for this sector of the Arctic.…”

“…(Heaton et al 2004 Nitrate stable isotopes and major ions in snow and ice, Svalbard C.P. Vega et al the period MarchÁApril, coincident with the highest incidence of Arctic Haze events at this sites (Morin et al 2007;Quinn et al 2007;Morin et al 2012; see also the Supplementary file). In contrast, [NO À 3 ] in central Greenland snow tends to peak during spring and summer rather than in autumn and winter, although seasonal variations are not always easy to resolve (Burkhart et al 2004;Hastings et al 2004).…”