Abstract. The atmospheric He/N₂ ratio is expected to be increasing due to the emission of He associated with fossil fuels and is expected to also vary in both space and time due to gravitational separation in the stratosphere. These signals may be useful indicators of fossil-fuel exploitation and variability in stratospheric circulation, but direct measurements of He/N₂ ratio are lacking on all time scales. Here we present a high-precision custom inlet system for mass spectrometers that continuously stabilizes the flow of gas during sample-standard comparison and removes all non-noble gases from the gas stream, enabling unprecedented accuracy in measurement of relative changes in the ⁴He/N₂ ratio. Repeat measurements of the same combination of high-pressure tanks using our inlet system achieves a reproducibility of ~ 10 per meg (i.e. 0.001 %) in 6–8 h analyses. This compares to interannual changes of He/N₂ gravitational enrichment at ~ 35 km in the mid latitude stratosphere of order 300–400 per meg, and an annual tropospheric increase from human fossil fuel activity of less than ~ 30 per meg y⁻¹ (bounded by previous work on helium isotopes). The gettering and flow-stabilizing inlet may also be used for the analysis of other noble gas isotopes and could resolve previously unobserved seasonal cycles in Kr/N₂ and Xe/N₂.

中文翻译：

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大气中He / N _2的测量，可作为化石燃料提取和平流层循环的指标

摘要。大气中He / N _2的比率由于与化石燃料相关的He的排放而有望增加，并且由于平流层中的重力分离，预期其时空也会变化。这些信号可能是化石燃料开采和平流层环流变化的有用指标，但是在所有时间尺度上都缺乏直接测量He / N ₂比的方法。在这里，我们提供了一种用于质谱仪的高精度定制入口系统，该系统在样品标准比较期间可连续稳定气流，并从气流中去除所有非惰性气体，从而实现⁴ He / N ₂比。使用我们的进气系统重复测量同一组高压储罐，在6–8小时的分析中，每兆升的重现性约为10（即0.001％）。相比之下，中纬度平流层〜35 km处He / N ₂重力富集的年际变化为每兆300–400，而人类化石燃料活动对流层的年增加量不到〜30每兆y ^-1（受先前关于氦同位素的研究的限制）。吸气和流量稳定的入口也可以用于分析其他稀有气体同位素，并且可以解决Kr / N ₂和Xe / N _2中以前未观察到的季节性周期。