A total of 10 boundary layer sampling events over the Pacific Ocean were analyzed for the purpose of defining the sea-to-air $CH_3$I flux using a mass balance photochemical model. These events were recorded on the National Center for Atmospheric Research (NCAR) C-130 aircraft as part of the Aerosol Charac-terization Experiment (ACE 1). The latitude range, covered by these events, was 2$^{circ}$ N to 55$^{circ}$ S. The flux ranges were 4 to 33 nmol m$^{-2}$ day$^{-1}$ , with an average value of 11$pm$8 nmol m$^{-2}$ day$^{-1}$ . This study also indicated that the current approach to estimate the flux was not systematically different from the sea-air exchange model.