The deuterium content of atmospheric molecular hydrogen: Method and initial measurements

• Published in: Journal of Geophysical Research, Washington, DC Washington, DC, 2000-11, Vol.105 (D21), p.26433-26445
• Main Authors: Gerst, Steve, Quay, Paul
• Format: Article
• Language: English
• Subjects: Chemical composition and interactions. Ionic interactions and processes; Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2000JD900387

A new technique for determining the δD of atmospheric molecular hydrogen (H2) at background mixing ratios is described in detail. An air sample is compressed into a high‐pressure cylinder, after which the cylinder is cooled to −196°C to condense the air and generate a headspace greatly enriched in H2. The H2‐enriched headspace is collected and admitted into a high‐vacuum extraction line, where the H2 is separated from the headspace gases by combustion to water followed by cryogenic collection. The H2‐derived water is then reduced back to H2 for measurement of its D/H content via isotope‐ratio mass spectrometry. The primary limitation of the method is contamination during compressor collection and subsequent storage of air samples in high‐pressure cylinders. The δD of atmospheric H2 was measured on air samples collected between 46°N and 72°S during a research cruise in the Pacific Ocean during 1998 and at Cheeka Peak, Washington (48°N), during 1997–1999 and Point Barrow, Alaska (71°N), during 1996–1997. These measurements yield a global average δD of atmospheric H2 of +130±4‰ and average Northern and Southern Hemispheric δD values of +123±3‰ and +138±8‰, respectively (versus Vienna standard mean ocean water).