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| Titel |
Oxygen isotope dynamics of atmospheric nitrate over the Antarctic plateau: First combined measurements of ozone and nitrate 17O-excess (Δ17O) |
| VerfasserIn |
William Vicars, Joel Savarino, Joseph Erbland, Susanne Preunkert, Bruno Jourdain, Markus Frey, Jaime Gil, Michel Legrand |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079539
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| Zusammenfassung |
| Variations in the isotopic composition of atmospheric nitrate (NO3-) provide novel indicators for important processes in boundary layer chemistry, often acting as source markers for reactive nitrogen (NOx = NO + NO2) and providing both qualitative and quantitative constraints on the pathways that determine its fate. Stable isotope ratios of nitrate (δ15N, δ17O, δ18O) offer direct insight into the nature and magnitude of the fluxes associated with different processes, thus providing unique information regarding phenomena that are often difficult to quantify from concentration measurements alone. The unique and distinctive 17O-excess (Δ17O = δ17O - 0.52 × δ18O ) of ozone (O3), which is transferred to NOx via oxidation reactions in the atmosphere, has been found to be 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 interpretations to the glacial/interglacial time scale using deep ice core records of nitrate.
Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C, Antarctica during December 2011 to January 2012. Sampling was conducted within the framework of the OPALE (Oxidant Production over Antarctic Land and its Export) project, thus providing an opportunity to combine our isotopic observations with a wealth of meteorological and chemical data, including in-situ concentration measurements of the gas-phase precursors involved in nitrate production (NOx, O3, OH, HO2, etc.). Furthermore, nitrate isotope analysis has been combined in this study for the first time with parallel observations of the transferrable Δ17O of surface ozone, which was measured concurrently at Dome C using our recently developed analytical approach. This unique dataset has allowed for a direct comparison of observed Δ17O(NO3-) values to those that are calculated solely from local measurements and invoke no assumptions regarding the Δ17O value of ozone and its transfer in the atmosphere. The predicted Δ17O signature for nitrate formed over the Antarctic plateau during OPALE is on the order of (21 ± 2) ‰ when production is assumed to occur only through the OH + NO2 pathway, which is expected to be the dominant formation channel during the continuously sunlit summer. This predicted value is much lower than the values measured for nitrate during OPALE, with observed Δ17O(NO3-) varying in the range of 27 - 31 ‰. This discrepancy between expected and observed Δ17O(NO3-) values suggests the existence of an unexpected process that contributes significantly to the atmospheric nitrate budget over Dome C. The relative merits of different potential explanations for this puzzling result will be discussed in the context of oxidation chemistry, air mass transport, and snow/atmosphere exchange. |
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