[A-AS21] 大気化学

[AAS21-20] 南極沿岸部における大気中硝酸の窒素・酸素安定同位体組成の季節変動

*石野 咲子¹、服部 祥平¹、カイロン ニコラ²、バルベロ アルバン²、ゴーティエ エルザ²、ジュールダン ブルーノ²、プリウンケルト スザンヌ²、レグランド ミシェル²、吉田 尚弘¹、サバリノ ジョエル² (1.東京工業大学大学院総合理工学研究科、2.グルノーブル大学/CNRS, LGGE, フランス)

キーワード：南極, エアロゾル, 硝酸, 安定同位体分析

Nitrate (NO₃^-) is the end-product of oxidation of nitrogen oxides (NO_X=NO+NO₂) in the atmosphere and one of the major ions preserved in Antarctic snow and ice. Therefore, there has been great interest in using concentration and isotopic signature of nitrate in ice cores to reconstruct past atmospheric NO_X sources and their oxidation processes to nitrate. For interpretation of nitrate records in Antarctic ice cores, it is necessary to know the long-term changes of concentration and isotopic compositions (¹⁵N/¹⁴N, ¹⁷O/¹⁶O and ¹⁸O/¹⁶O) of nitrate in the atmosphere which deposits on the surface snow. In this study, we present seasonal variation of nitrogen and triple oxygen isotopic composition of nitrate collected at French Antarctic Station Dumont d'Urville (66^o40'S, 140^o01'E) throughout the year 2011. The significant increase of nitrate concentration during spring and summer period was observed and ¹⁵N were depleted in the nitrates, indicating that there was the substantial NO_X input to the atmosphere by photolysis of nitrate in the surface snow. In addition, relatively low ¹⁷O excess in summer period suggests that NO_X oxidation to nitrate by OH radicals was increased. On the other hand, high ¹⁷O excess with low concentration in fall and winter period suggests that OH oxidation pathway was depleted and other oxidation pathways related to O₃ were dominant. Additionally, the small nitrate increase in winter period might be attributed to the transport of stratospheric nitrate to troposphere due to the formation of polar stratospheric clouds. In the presentation, we will discuss the long-term change of the seasonal trends and compare the result with that of 2001 year-round isotopic analysis using nitrate aerosols at the same station.