Computer Science
Scientific paper
Jul 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002gecoa..66.2475r&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 66, Issue 14, pp.2475-2481
Computer Science
18
Scientific paper
We present the results of a study of the concentration and D/H ratio of molecular hydrogen from air in the Los Angeles Basin and adjacent San Gabriel Mountains. These data define a mixing relationship in dimensions of D/H ratio vs. 1/(H 2 ) which constrains the D VSMOW of unpolluted winter air in this region to be ca. +100 to +125 and that of urban H 2 sources to be ca. -270 . This study makes use of a new method for measuring the deuterium content of molecular hydrogen in small samples (~100 to 500 cc) of air, which we describe in detail. The method consists of an off-line separation of H 2 followed by introduction to the mass spectrometer in a continuous flow of He. Off-line, all components of an atmospheric gas sample, with the exception of He, H 2 , and Ne are condensed by exposure to a cold-trap held at 30 Kelvin. This separation is followed by cryo-transfer of non-condensable gases to a small volume molecular sieve finger, with assist from a mercury piston pump. At the mass spectrometer, the sample is put in line with a continuous flow of He where it is focused on to an additional column of molecular sieve before subsequent introduction into the ion source. Analyses of DH/H 2 ratio have accuracy and precision of ±4 to 7 per mil. Comparison of sample peak area to peak areas of standards of known size allows for determination of H 2 concentration with accuracy and precision of ~±5%, relative. The method reduces sample size and processing time by several orders of magnitude compared to previous methods, allowing for sampling at proportionately higher spatial and temporal resolution.
Eiler John
Kitchen Nami
Rahn Thom
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