Quantifying the contribution of marine organic gases to atmospheric iodine

Oceanic emissions of gaseous organic iodine-atom precursors have the potential to significantly affect atmospheric chemistry and climate, however there is currently considerable uncertainty associated with quantifying their sources. We present sea-air fluxes calculated from simultaneous air and seawater measurements of a comprehensive range of volatile organic iodine compounds (VOICs), including CH3I and the less commonly reported dihalomethanes CH2ICl, CH2IBr and CH2I2, made during two cruises in the Atlantic Ocean between 15-58 degrees N. The combined dihalomethane flux provides a global iodine source (similar to 0.33 +/- 0.19 Tg I y(-1)) comparable to that of CH3I, and a surface iodine atom source 3-4 times higher. However, a 1D atmospheric model reveals that, in the tropical east Atlantic Ocean in the vicinity of Cape Verde, even these combined VOIC fluxes are capable of supporting only similar to 10-25% of the observed IO levels, and suggests that a substantial (340-640 nmol I m(-2) d(-1)) additional photochemical source of iodine is required. Citation: Jones, C. E., K. E. Hornsby, R. Sommariva, R. M. Dunk, R. von Glasow, G. McFiggans, and L. J. Carpenter (2010), Quantifying the contribution of marine organic gases to atmospheric iodine, Geophys. Res. Lett., 37, L18804, doi: 10.1029/2010GL043990.