The sea-to-air flux of a VOC can be calculated from the following equation:where V is the gas transfer velocity (cm s -1 ), which depends on wind speed; pVOC water and pVOC air are the partial pressures of the VOC in water and air, respectively; and K H is the Henry's law constant for the VOC. The gas transfer velocity can be calculated from the Wanninkhof (1992) formulation as followswhere u is the wind speed and Sc is the Schmidt number.The K H values for chlorofluorocarbons CFC-11 and CFC-12 (which are used as tracers to track the history of deep seawater previously exposed to the atmosphere) as functions of seawater temperature and salinity have been reported by several investigators (Hunter-Smith et al., 1983;Warner and Weiss, 1985;Wisegarver and Cline, 1985), and values for some halocarbons (e.g., CH 3 I, CH 2 Br 2 , and CH 2 ClI) in seawater have also been reported (HunterSmith et al., 1983;Elliott and Rowland, 1993;Gossett, 1987;Moore et al., 1995;Moore, 2000 The sea-to-air flux of C 2 H 5 I (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 2 H 5 I in surface seawater and air. The values of K H , defined as the ratio of molar concentration (mol l -1 ) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFCl 3 (CFC-11), C 5 H 8 (isoprene), C 2 H 2 F 4 (HFC-134a), CHF 2 Cl (HCFC-22), CH 3 I, CH 2 Br 2 , C 2 H 5 I, CH 2 Cl 2 , CH 2 ClI, 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 2 H 5 I and C 5 H 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 2 H 5 I 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 2 H 5 I 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.