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Active chlorine in the remote marine boundary layer: Modeling anomalous measurements of δ 13 C in methane
Author(s) -
Allan W.,
Lowe D. C.,
Cainey J. M.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013064
Subject(s) - sink (geography) , methane , northern hemisphere , fractionation , atmospheric sciences , chlorine , atmospheric methane , troposphere , isotope fractionation , dimethyl sulfide , annual cycle , environmental science , environmental chemistry , chemistry , climatology , geology , sulfur , cartography , organic chemistry , geography
Measurements of δ 13 C in methane in the marine boundary layer (MBL) of the extratropical Southern Hemisphere imply a kinetic isotope fractionation much larger than would be expected if the hydroxyl radical were the only tropospheric methane sink. We use a simple chemical box model to show that the assumption of a MBL active chlorine (Cl • ) sink can explain these anomalous observations provided there is a seasonal cycle in the Cl • sink with a summer‐winter concentration difference ∼ 6 · 10³ cm −3 . The required summer maximum and yearly mean Cl • concentrations are plausible, and imply a global Cl • sink strength for methane of < 5 Tg yr −1 . Choice of a Cl • sink seasonal cycle linked to the nonsinusoidal dimethyl sulfide seasonal cycle gives the observed fractionation with a smaller yearly mean Cl • concentration than equivalent sinusoidal Cl • cycles.