Dataset Information

Measurement of ¹⁸ O¹⁸ O and ¹⁷ O¹⁸ O in atmospheric O₂ using the 253 Ultra mass spectrometer and applications to stratospheric and tropospheric air samples.

ABSTRACT:

Rationale

The doubly substituted isotopologues (e.g., ¹⁸ O¹⁸ O, ¹⁷ O¹⁸ O) in atmospheric O₂ are potential tracers for ozone photochemistry and atmospheric temperatures. Their low abundances and isobaric interference are the major analytical challenges. The 253 Ultra high-resolution stable isotope ratio mass spectrometer is suitable for resolving isobaric interferences.

Methods

O₂ from air is purified using gas chromatography on a packed column filled with molecular sieve 5 Å and cooled to -78°C. The δ¹⁷ O, δ¹⁸ O, Δ¹⁷ O, Δ₃₅ and Δ₃₆ values are measured on the extracted O₂ with the 253 Ultra at medium mass resolution (M/ΔM ~10000) using Faraday detectors for the singly substituted isotopologues and ion counters for the doubly substituted isotopologues.

Results

Interferences from isobars, mainly ³⁵ Cl for ¹⁷ O¹⁸ O and H³⁵ Cl and ³⁶ Ar for ¹⁸ O¹⁸ O, are sufficiently resolved to enable high-precision determination of Δ₃₅ and Δ₃₆ . The Δ₃₅ and Δ₃₆ values of O₂ after photochemical isotope equilibration at -63°C and heating to 850°C agree with the theoretical prediction. The stratospheric Δ₃₅ and Δ₃₆ values are close to isotopic equilibrium at the ambient temperatures. However, the values for tropospheric O₂ differ from those expected at equilibrium.

Conclusions

The 253 Ultra allows interference-free clumped isotope measurements of O₂ at medium mass resolution. The Δ₃₅ and Δ₃₆ signatures in atmospheric O₂ are mainly governed by O₃ photochemistry, temperature and atmospheric transport. Tropospheric O₂ is isotopically well mixed and retains a significant stratospheric signature.

SUBMITTER: Laskar AH

PROVIDER: S-EPMC6594091 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Dataset Information

Measurement of ¹⁸ O¹⁸ O and ¹⁷ O¹⁸ O in atmospheric O₂ using the 253 Ultra mass spectrometer and applications to stratospheric and tropospheric air samples.

Rationale

Methods

Results

Conclusions

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Measurement of ¹⁸ O¹⁸ O and ¹⁷ O¹⁸ O in atmospheric O₂ using the 253 Ultra mass spectrometer and applications to stratospheric and tropospheric air samples.