Articles | Volume 16, issue 4
Atmos. Chem. Phys., 16, 2659–2673, 2016

Special issue: Oxidant Production over Antarctic Land and its Export...

Atmos. Chem. Phys., 16, 2659–2673, 2016

Research article 03 Mar 2016

Research article | 03 Mar 2016

Oxygen isotope mass balance of atmospheric nitrate at Dome C, East Antarctica, during the OPALE campaign

Joël Savarino1,2, William C. Vicars1,2,a, Michel Legrand1,2, Suzanne Preunkert1,2, Bruno Jourdain1,2, Markus M. Frey3, Alexandre Kukui4,5, Nicolas Caillon1,2, and Jaime Gil Roca4,5 Joël Savarino et al.
  • 1Université Grenoble Alpes, Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), 38000 Grenoble, France
  • 2CNRS, Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), 38000 Grenoble, France
  • 3British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
  • 4Laboratoire Atmosphère, Milieux et Observations Spatiales (LATMOS), UMR8190, CNRS-Université de Versailles Saint Quentin, Université Pierre et Marie Curie, Paris, France
  • 5Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), UMR6115 CNRS-Université d'Orléans, 45071 Orléans CEDEX 2, France
  • anow at: Technical Services Program, Air Pollution Control Division, Colorado Department of Public Health and Environment, Denver, CO, USA

Abstract. Variations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO2 = NOx). The unique and distinctive 17O excess (Δ17O = δ17O − 0.52 × δ18O) of ozone, which is transferred to NOx via oxidation, is a particularly useful isotopic fingerprint in studies of NOx transformations. Constraining the propagation of 17O excess within the NOx cycle is critical in polar areas, where there exists the possibility of extending atmospheric investigations to the glacial–interglacial timescale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic Plateau) during the austral summer of 2011/2012. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NOx, O3, OH, HO2, RO2, etc.) and direct observations of the transferrable Δ17O of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO2 pathway and using concurrent measurements of OH and NO2, we calculated a Δ17O signature for nitrate on the order of (21–22 ± 3) ‰. These values are lower than the measured values that ranged between 27 and 31 ‰. This discrepancy between expected and observed Δ17O(NO3) values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this East Antarctic region. However, systematic errors or false isotopic balance transfer functions are not totally excluded.

Short summary
Atmospheric nitrate is collected on the East Antarctic ice sheet. Nitrogen and oxygen stable isotopes and concentrations of nitrate are measured. Using a box model, we show that there is s systematic discrepancy between observations and model results. We suggest that this discrepancy probably results from unknown NOx chemistry above the Antarctic ice sheet. However, possible misconception in the stable isotope mass balance is not completely excluded.
Final-revised paper