Determination of Henry's law constant of halocarbons in seawater and analysis of sea-to-air flux of iodoethane (C_2H_5I) in the Indian and Southern oceans based on partial pressure measurements

摘要

The sea-to-air flux of C_2H_5I (iodoethane) in the Indian Ocean and the Southern Ocean was estimated from the Henry's law constant (K_H) and the measured partial pressures of C_2H_5I in surface seawater and air. The values of K_H, defined as the ratio of molar concentration (moll~(-1)) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFC1_3 (CFC-11), C_5H_8 (isoprene), C_2H_2F_4 (HFC-134a), CHF_2C1 (HCFC-22), CH_3I, CH_2Br_2, C_2H_5I, CH_2Cl_2, CH_2CII, and CHBr_3) 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 K_H values for C_2H_5I and C_5H_8 as functions of temperature. The K_H values for the other VOCs were in good agreement with previously reported values. We calculated the sea-to-air flux of C_2H_5I using the newly determined K_H. Large sea-to-air fluxes (average, 0.04 nmol m~(-2)h~(-1)) were widespread in the Southern Ocean. We suggest that high biological productivity led to a high rate of C_2H_5I 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.