Open AccessIsotopic composition of H 2 from CH 4 oxidation in the stratosphere and the troposphere
Author(s) -
Rhee Tae Siek,
Brenninkmeijer Carl A. M.,
Braß Marc,
Brühl Christoph
Publication year - 2006
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005jd006760
Subject(s) - stratosphere , troposphere , photodissociation , fractionation , deuterium , oxidizing agent , isotope fractionation , yield (engineering) , kinetic isotope effect , chemistry , photochemistry , analytical chemistry (journal) , atmospheric sciences , environmental chemistry , materials science , geology , physics , atomic physics , organic chemistry , metallurgy
Enrichment in deuterium (D) of stratospheric H 2 is investigated using new and published data. Applying a Rayleigh model to account for the isotopic fractionations in the photochemical chain reactions from CH 4 to the final product H 2 O via H 2 reveals a strong enrichment of photochemically produced H 2 . This is consistent with previous studies, but the degree of enrichment obtained in this study appears to be 100–120‰ larger than the previous estimates on average. The discrepancy primarily stems from the former use of either an isotopic fractionation factor of H 2 that does not take into account the effect of stratospheric transport or an H 2 yield from CH 2 O photolysis that is not applicable to stratospheric conditions. We further investigate the same isotopic fractionation process under tropospheric conditions by considering the differences in both the species and amounts of oxidizing agents and the wavelengths that are effective in the photolysis of CH 2 O. These were not considered in the former studies when they derived the δ D value under the tropospheric conditions. We thereby anticipate the δ D value of H 2 from photochemical oxidation of CH 4 in the troposphere to be 190 (±50)‰.