Temporal and latitudinal distributions of stratospheric N2O isotopomers
Temporal and latitudinal distributions of stratospheric N2O isotopomers
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平流层 N2O 同位素异构体的时间和纬度分布
DOI：
10.1029/2003jd004316
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发表时间：
2004
影响因子：
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通讯作者：
H. Honda
中科院分区：
文献类型：
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作者：
S. Toyoda;N. Yoshida;T. Urabe;Y. Nakayama;Takeshi Suzuki;Kazuhide Tsuji;K. Shibuya;S. Aoki;T. Nakazawa;S. Ishidoya;K. Ishijima;S. Sugawara;T. Machida;G. Hashida;S. Morimoto;H. Honda
[1]在1990 - 2001年期间，在日本（39°N，142°E）、瑞典（68°N，20°E）和南极洲（69°N，40°E）的平流层中观测到N2 O同位素垂直廓线的时间和纬度变化。用球载低温采样器采集样品，并在实验室用质谱法进行分析。在平流层低层（低于1022公里），较重同位素（15 N14 N16 O、14 N15 N16 O和14 N14 N18 O）相对于14 N14 N16 O的富集因子几乎不变，但在较高的高度（1022 -35公里）增加，同时显示出季节和纬度差异。在实验室实验中还获得了N_2O光解和光氧化过程中的富集因子，并与观测结果进行了比较。我们发现，在较高的海拔地区（1）分馏的同位素主要是由光解，但也受到物理过程的影响，（2）在冬季极涡的空气质量的下沉引起的平流层上部的空气质量的入侵，在N2 O耗尽，（3）在当地的春天涡的衰减导致中纬度空气质量的快速水平平流。在较低的高度，同位素比例是由平流层内或平流层与对流层之间的光解、光氧化和空气质量混合决定的。在11年期间，在日本未检测到同位素分布的长期趋势。假定中纬度平流层低层空气与对流层交换，估算了平流层N_2O“回流”的同位素比值。这些值可以用于同位素质量平衡模型，以限制全球N2 O预算。
[1] Temporal and latitudinal variations of vertical profiles of N2O isotopomers were observed in the stratosphere over Japan (39°N, 142°E), Sweden (68°N, 20°E), and Antarctica (69°N, 40°E) during the period between 1990 and 2001. Samples were collected with a balloon-borne cryogenic sampler and analyzed by mass spectrometry in the laboratory. Observed enrichment factors for heavier isotopomers (15N14N16O, 14N15N16O, and 14N14N18O) relative to 14N14N16O were nearly constant in the lower stratosphere (less than ∼22 km) but increased at higher altitudes (∼22–35 km) while showing seasonal and latitudinal differences. Enrichment factors during the photolysis and photo-oxidation of N2O were also obtained in laboratory experiments and compared with those observed. We found that in the higher-altitude region (1) fractionation of the isotopomers is mainly determined by photolysis, but is also affected by physical processes, (2) subsidence of air masses in the winter polar vortex induces the intrusion of an upper stratospheric air mass depleted in N2O, and (3) decay of the vortex in the local spring leads to rapid horizontal advection of midlatitude air masses. At lower altitudes, isotopomer ratios are determined by photolysis, photo-oxidation, and the mixing of air masses within the stratosphere or between the stratosphere and the troposphere. Secular trend of isotopomer profiles was not detectable over Japan during 11 years. Assuming that the lower stratospheric air over midlatitudes is exchanged with the troposphere, isotopomer ratios of the N2O “back-flux” from the stratosphere were estimated. These values can be used in the isotopomeric mass balance model to constrain the global N2O budget.