TERRAPUB Geochemical Journal
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Geochemical Journal, Vol. 45 (No. 2), pp. e1-e7, 2011

EXPRESS LETTER

Determination of Henry's law constant of halocarbons in seawater and analysis of sea-to-air flux of iodoethane (C2H5I) in the Indian and Southern oceans based on partial pressure measurements

Atsushi Ooki and Yoko Yokouchi

National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan

(Received December 6, 2010; Accepted February 25, 2011; Online published March 9, 2011)

Abstract: The sea-to-air flux of C2H5I (iodoethane) in the Indian Ocean and the Southern Ocean was estimated from the Henry's law constant (KH) and the measured partial pressures of C2H5I in surface seawater and air. The values of KH, defined as the ratio of molar concentration (mol l-1) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFCl3 (CFC-11), C5H8 (isoprene), C2H2F4 (HFC-134a), CHF2Cl (HCFC-22), CH3I, CH2Br2, C2H5I, CH2Cl2, CH2ClI, and CHBr3) were measured with an equilibrator and a purge-and-trap system in combination with gas chromatography-mass spectrometry. Ours is the first report of the KH values for C2H5I and C5H8 as functions of temperature. The KH values for the other VOCs were in good agreement with previously reported values. We calculated the sea-to-air flux of C2H5I using the newly determined KH. Large sea-to-air fluxes (average, 0.04 nmol m-2h-1) were widespread in the Southern Ocean. We suggest that high biological productivity led to a high rate of C2H5I production in the subpolar water, and that the strong winds that frequently blow over the Southern Ocean resulted in the large sea-to-air flux.
Key words: solubility, equilibrator, volatile organic compounds, isoprene, ethyl iodide


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