Probing stratospheric transport and chemistry with new balloon and aircraft observations of the meridional and vertical N2O isotope distribution
Probing stratospheric transport and chemistry with new balloon and aircraft observations of the meridional and vertical N2O isotope distribution
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DOI：
10.5194/acp-6-3535-2006
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发表时间：
2006-08-30
影响因子：
6.3
通讯作者：
Roeckmann, T.
中科院分区：
文献类型：
--
作者：
Kaiser, J.;Engel, A.;Roeckmann, T.
分析了一套完整的平流层气球和飞机样品，分析了一氧化二氮(N2O)的位置相关同位素组成。报告给出了1987至2003年间总共220个样品的结果，几乎是迄今发表的平流层N2O同位素质谱学测量结果的三倍。低温气球样品是在极地(基律纳/瑞典，北纬68度)、中纬度(法国南部，北纬44度)和热带地点(海德拉巴/印度，北纬18度)获得的。在2003年EUPLEX宣传活动期间，在高空飞机M55GePhysica上使用新开发的全空气采样器采集了飞机样本。当混合比大于200nmol(-1)时，相对同位素丰度(增量值)与混合比表现出紧密的关系，这种关系与纬度和季节几乎无关，可以用瑞利分馏或混合来解释。然而，当混合比低于200nmolmol(-1)时，这种紧密关系被经向变化、季节变化和年际变化所取代。与以前公布的中纬度气球廓线相比，甚至显示出很大的纬向变化，这证明使用三维(3-D)模型进行进一步数据解释是合理的。一般来说，视分馏常数(即视同位素效应)的大小随着海拔的升高而不断增加，从赤道到北极则不断减小。只有后一种观测结果才能通过N2O光化学和瑞利分馏框架中输运的时间尺度之间的相互作用来定性地理解。当极地涡旋空气与几乎不含N2O的平流层上层/中层空气混合时(例如，在2003年北方冬季，可能在1992年)，也会发生偏离瑞利分馏行为的情况。在混合比低于200nmolmo1(-1)的极地涡旋中的飞机观测结果偏离了瑞利分馏和两端混合的预期同位素变化，但可以用涡内和涡外空气之间持续的弱混合来解释(Plumb等人，2000年)。然而，似乎这里描述的所有简单方法都不能捕捉到平流层N2O同位素分布的所有特征，这再次证明了使用3-D模型的合理性。O-18/O-16与平均N-15/N-14同位素比值或与位置相关的N-15/N-14同位素比值的相关性表明，光氧化作用对平流层下部N2O汇的贡献很大(当N2O混合比大于300nmol(-1)时，可能达到100%)。对于更高的海拔，这些同位素相关性的温度依赖性在平流层观测中变得可见。
A comprehensive set of stratospheric balloon and aircraft samples was analyzed for the position-dependent isotopic composition of nitrous oxide (N2O). Results for a total of 220 samples from between 1987 and 2003 are presented, nearly tripling the number of mass-spectrometric N2O isotope measurements in the stratosphere published to date. Cryogenic balloon samples were obtained at polar (Kiruna/Sweden, 68 degrees N), mid-latitude ( southern France, 44 degrees N) and tropical sites (Hyderabad/India, 18 degrees N). Aircraft samples were collected with a newly-developed whole air sampler on board of the high-altitude aircraft M55 Geophysica during the EUPLEX 2003 campaign. For mixing ratios above 200 nmol mol(-1), relative isotope enrichments (delta values) and mixing ratios display a compact relationship, which is nearly independent of latitude and season and which can be explained equally well by Rayleigh fractionation or mixing. However, for mixing ratios below 200 nmol mol(-1) this compact relationship gives way to meridional, seasonal and interannual variations. A comparison to a previously published mid-latitude balloon profile even shows large zonal variations, justifying the use of three-dimensional (3-D) models for further data interpretation.In general, the magnitude of the apparent fractionation constants (i.e., apparent isotope effects) increases continuously with altitude and decreases from the equator to the North Pole. Only the latter observation can be understood qualitatively by the interplay between the time-scales of N2O photochemistry and transport in a Rayleigh fractionation framework. Deviations from Rayleigh fractionation behavior also occur where polar vortex air mixes with nearly N2O-free upper stratospheric/mesospheric air ( e. g., during the boreal winters of 2003 and possibly 1992). Aircraft observations in the polar vortex at mixing ratios below 200 nmol mol(-1) deviate from isotope variations expected for both Rayleigh fractionation and two-end-member mixing, but could be explained by continuous weak mixing between intravortex and extravortex air ( Plumb et al., 2000). However, it appears that none of the simple approaches described here can capture all features of the stratospheric N2O isotope distribution, again justifying the use of 3-D models. Finally, correlations between O-18/O-16 and average N-15/N-14 isotope ratios or between the position-dependent N-15/N-14 isotope ratios show that photo-oxidation makes a large contribution to the total N2O sink in the lower stratosphere ( possibly up to 100% for N2O mixing ratios above 300 nmol mol(-1)). Towards higher altitudes, the temperature dependence of these isotope correlations becomes visible in the stratospheric observations.