1978-2011年期间地球大气中氦和其他惰性气体的浓度和同位素比
Concentrations and isotope ratios of helium and other noble gases in the Earth's atmosphere during 1978-2011
摘要：
在过去几十年中，大气层惰性气体成分的演变几乎没有得到研究，因为与许多其他大气层气体相比，没有系统的时间序列测量。基于理论上的考虑，大气惰性气体同位素组成被假定为在长达10^6年的时间尺度上是稳定的，除了预测的He浓度和3 He/4 He比的人为变化的潜在例外。然而，在大气中的He同位素组成的预测变化的实验评估是有争议的。为了对这些假设和预测进行实证检验，我们分析了格里姆角空气档案馆（一个明确的南半球海洋边界层空气档案馆）样本中的惰性气体同位素组成。由此得到的1978-2011年期间20 Ne、40 Ar、86 Kr和136 Ne浓度以及20 Ne/22 Ne和40 Ar/36 Ar比值的时间序列表明，在这段时间间隔内，大气Ne、Ar、Kr和136 Ne的组成是稳定的。He同位素数据提供了强有力的证据，在同一时间间隔内，3 He/4 He的减少，平均速率为0.23-0.30 permil每年。这一结果与大多数模型预测的与矿物燃料的开采和燃烧有关的大气中3 He/4 He比率的下降速率是一致的。
英文摘要：
The evolution of the atmospheric noble gas composition during the past few decades has hardly been studied because, in contrast to many other atmospheric gases, systematic time-series measurements have not been available. Based on theoretical considerations, the atmospheric noble gas isotope composition is assumed to be stable on time scales of up to about 10^6 years, with the potential exception of anthropogenic changes predicted for the He concentration and the 3He/4He ratio. However, experimental assessments of the predicted changes in the atmospheric He isotope composition are controversial. To empirically test these assumptions and predictions, we analysed the noble gas isotope composition in samples of the Cape Grim Air Archive, a well-defined archive of marine boundary layer air in the southern hemisphere. The resulting time series of the 20Ne, 40Ar, 86Kr and 136Xe concentrations and 20Ne/22Ne and 40Ar/36Ar ratios during 1978-2011 demonstrate the stability of the atmospheric Ne, Ar, Kr and Xe composition during this time interval. The He isotope data provide strong evidence for a decrease in the 3He/4He during the same time interval at a mean rate of 0.23-0.30 permil per year. This result is consistent with most model predictions of the rate of decrease in the atmospheric 3He/4He ratio associated with mining and burning of fossil fuels.
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