Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 5 2006 10.5194/acpd-6-8817-2006 http://www.atmos-chem-phys-discuss.net/6/8817/2006/ http://www.atmos-chem-phys-discuss.net/6/8817/2006/acpd-6-8817-2006.html http://www.atmos-chem-phys-discuss.net/6/8817/2006/acpd-6-8817-2006.pdf 8817 8870 2006-09-21 Nitrogen and oxygen isotopic constraints on the origin of atmospheric nitrate in coastal Antarctica J. Savarino J. Kaiser S. Morin D. M. Sigman M. H. Thiemens Laboratoire de Glaciologie et Géophysique de l’Environnement (CNRS – UJF), 54 rue Molière BP96, St Martin d’Hères, 38402 France Princeton University, Department of Geosciences, Princeton, NJ 08544, USA University of California at San Diego, Department of Chemistry and Biochemistry, 9500 Gilman Drive, La Jolla, CA 92093-0356, USA now at: University of East Anglia, School of Environmental Sciences, Norwich, Norfolk, NR4 7TJ, UK Throughout the year 2001, size-segregated aerosol samples were collected continuously for 10 to 15 days at the French Antarctic Station Dumont d'Urville (DDU) (66°40' S, l40°01' E, 40 m above mean sea level). The nitrogen and oxygen isotopic ratios of particulate nitrate at DDU exhibit seasonal variations that are among the most extreme observed for nitrate on Earth. Associated with a late winter increase in the concentration of particulate nitrate, δ¹⁸O and Δ¹⁷O reach as high as 111.5 versus VSMOW and 41.1, respectively. These are best explained as a signal of stratospheric input, with halogen radicals extracting 17O- and 18O-rich terminal oxygen from ozone and incorporating it into the nitrogen oxides, even if we are unable to reproduce this high Δ¹⁷O value with the current knowledge of isotopic anomaly transfers during chemical reactions. This failure calls for the evaluation of polar ozone isotopic composition. During the late springtime peak in particulate nitrate, its δ¹⁵N falls to −46.9 versus atmospheric N₂, suggesting that this peak results from snow re-emission, which has been shown previously to enrich in δ¹⁵N the retained nitrate fraction in continental Antarctic sites.