# A method for resolving changes in atmospheric He ∕ N 2 as an indicator of fossil fuel extraction and stratospheric circulation

The atmospheric inline-formula $M4inlinescrollmathmlchem\mathrm{normal He}/{\mathrm{normal N}}_{normal 2}$ 35pt14ptsvg-formulamathimgd38d2e975d71d5b9423ca4fdbbd12db9 amt-14-2515-2021-ie00004.svg35pt14ptamt-14-2515-2021-ie00004.png ratio is expected to increase 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 inline-formula $M5inlinescrollmathmlchem\mathrm{normal He}/{\mathrm{normal N}}_{normal 2}$ 35pt14ptsvg-formulamathimg7606266f310c20a7e405bef9d50dc7b3 amt-14-2515-2021-ie00005.svg35pt14ptamt-14-2515-2021-ie00005.png ratio are lacking on all timescales. 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. This enables unprecedented accuracy in measurement of relative changes in the helium mole fraction, which can be directly related to the inline-formula4inline-formula $M7inlinescrollmathmlchem\mathrm{normal He}/{\mathrm{normal N}}_{normal 2}$ 35pt14ptsvg-formulamathimg805c4d9784ac0525fee662c2c569736f amt-14-2515-2021-ie00006.svg35pt14ptamt-14-2515-2021-ie00006.png ratio using supplementary measurements of inline-formula $M8inlinescrollmathmlchem{\mathrm{normal O}}_{normal 2}/{\mathrm{normal N}}_{normal 2}$ 34pt14ptsvg-formulamathimg4429455449d1e061d22bb9828b35172e amt-14-2515-2021-ie00007.svg34pt14ptamt-14-2515-2021-ie00007.png , inline-formula $M9inlinescrollmathmlchem\mathrm{normal Ar}/{\mathrm{normal N}}_{normal 2}$ 32pt14ptsvg-formulamathimg8ae0a88765137c85d96a7f62a8f988cf amt-14-2515-2021-ie00008.svg32pt14ptamt-14-2515-2021-ie00008.png and COinline-formula2. Repeat measurements of the same combination of high-pressure tanks using our inlet system achieves a inline-formula $M11inlinescrollmathmlchem\mathrm{normal He}/{\mathrm{normal N}}_{normal 2}$ 35pt14ptsvg-formulamathimg887dcc6587835d80ce5e1d90c66606dc amt-14-2515-2021-ie00009.svg35pt14ptamt-14-2515-2021-ie00009.png reproducibility of inline-formula∼ 10 per meg (i.e., 0.001 %) in 6–8 h analyses. This compares to interannual changes of gravitational enrichment at inline-formula∼ 35 km in the midlatitude stratosphere of order 300–400 per meg and an annual tropospheric increase from human fossil fuel activity of less than inline-formula∼ 30 per meg yrinline-formula−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 inline-formula $M16inlinescrollmathmlchem\mathrm{normal Kr}/{\mathrm{normal N}}_{normal 2}$ 32pt14ptsvg-formulamathimg0a381b4505ab18ad51705371a2c23729 amt-14-2515-2021-ie00010.svg32pt14ptamt-14-2515-2021-ie00010.png and inline-formula $M17inlinescrollmathmlchem\mathrm{normal Xe}/{\mathrm{normal N}}_{normal 2}$ 34pt14ptsvg-formulamathimg2d21453408ba83e9e6574b999635ca4d amt-14-2515-2021-ie00011.svg34pt14ptamt-14-2515-2021-ie00011.png .

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Birner, Benjamin / Paplawsky, William / Severinghaus, Jeffrey / et al: A method for resolving changes in atmospheric He ∕ N2 as an indicator of fossil fuel extraction and stratospheric circulation. 2021. Copernicus Publications.

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