HR: 0800h
AN: A21C-0886    [Abstracts]
TI: A year-round isotopic survey of aerosol nitrate from a coastal Antarctic station
AU: * Savarino, J
EM: jsavarino@lgge.obs.ujf-grenoble.fr
AF: Laboratoire de Glaciologie et Geophysique de l'Environnement, 54 rue Moliere BP96, St Martin d'Heres, 38402 France
AU: Morin, S
EM: morin@lgge.obs.ujf-grenoble.fr
AF: Laboratoire de Glaciologie et Geophysique de l'Environnement, 54 rue Moliere BP96, St Martin d'Heres, 38402 France
AU: Kaiser, J
EM: kaiser@Princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Thiemens, M H
EM: mht@chem.ucsd.edu
AF: University of California, San Diego, Dept Chemistry & Biochemistry 9500 Gilman Drive, La Jolla, CA 92093-0356 United States
AB: The source and origin of nitrate in Antarctica is still an unresolved issue. Due to the remoteness of the Antarctic continent, the most probable sources of nitrate must be inputs from the stratosphere and nitrate associated with tropospheric biomass burning and lightning. Identifying and quantifying these sources will improve our understanding of the atmospheric N cycle and help solve the interpretation of nitrate ice core records. Size-segregated aerosols were collected at Dumont D'Urville in 2000-2001 (latitude 66° 40S, longitude 140° 01E, 40 m asl) at a sampling rate of one sample/week using a HiVol aerosol collector, equipped with a 4-stage cascade impactor. Nitrate was extracted in two particle sizes (lower and higher than 1 um) and analyzed for δ¹⁵N, δ¹⁸O and Δ¹⁷O. No fundamental isotopic difference exists between coarse and fine mode for ¹⁵N, and ¹⁸O, suggesting that gas to particle conversion is not a major factor controlling the oxygen and nitrogen isotopic composition of nitrate. However, episodic differences are sometimes observed between these two size modes for ¹⁸O and particularly for Δ¹⁷O. Observations confirm the strong season cycle of δ¹⁵N, first observed by Wagenbach et al., (1998), with values ranging from 20 to -36‰. The maximum value is reached at the end of August and is followed by a constant decrease until the minimum is reached at the beginning of November and then δ¹⁵N rises again. This timing strongly supports the idea of a seasonal cycle controlled by the sedimentation of PSC. Oxygen isotopes range from 61 to 107‰ and from 18 to 40‰ for ¹⁸O and Δ¹⁷O, respectively. A particularity of oxygen isotopes, beyond its seasonal cycle, is the bimodal peak shape of the profile, with the first and second maximum at mid April and mid August, respectively. Interestingly, the maximum of the Δ¹⁷O is reached when the ¹⁵N peaks in August, a possible consequence of nighttimes NOx chemistry which favours the ozone over OH oxidation (Michalski and Thiemens, 2003). However, detailed comparisons with the local chemistry, meteorology and stratospheric lidar sounding should first be performed before any definitive conclusion can be drawn. To our knowledge, the N and O isotopic composition of Antarctic atmospheric nitrate represents the most extreme values observed so far.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0365 Troposphere: composition and chemistry
DE: 0469 Nitrogen cycling
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005