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D/H ratios of atmospheric H_2 in urban air: Results using new methods for analysis of nano-molar H_2 samples

Rahn, Thom and Kitchen, Nami and Eiler, John (2002) D/H ratios of atmospheric H_2 in urban air: Results using new methods for analysis of nano-molar H_2 samples. Geochimica et Cosmochimica Acta, 66 (14). pp. 2475-2481. ISSN 0016-7037. doi:10.1016/S0016-7037(02)00858-X. https://resolver.caltech.edu/CaltechAUTHORS:20121023-114246813

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Abstract

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 δD_(VSMOW) of unpolluted winter air in this region to be ca. +100 to +125 ‰ and that of urban H2 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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/S0016-7037(02)00858-XDOIUNSPECIFIED
http://www.sciencedirect.com/science/article/pii/S001670370200858XPublisherUNSPECIFIED
Additional Information:© 2002 Elsevier Science Ltd. Received August 14, 2001; accepted in revised form January 31, 2002. We thank Mike Brown and Antonin Bouchez for sample collection on Haleakala. Associate editor: T.E. Cerling.
Issue or Number:14
DOI:10.1016/S0016-7037(02)00858-X
Record Number:CaltechAUTHORS:20121023-114246813
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20121023-114246813
Official Citation:Thom Rahn, Nami Kitchen, John Eiler, D/H ratios of atmospheric H2 in urban air: results using new methods for analysis of nano-molar H2 samples, Geochimica et Cosmochimica Acta, Volume 66, Issue 14, 15 July 2002, Pages 2475-2481, ISSN 0016-7037, 10.1016/S0016-7037(02)00858-X. (http://www.sciencedirect.com/science/article/pii/S001670370200858X)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35037
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:23 Oct 2012 20:04
Last Modified:09 Nov 2021 23:12

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