Coastal zone production of IO precursors: A 2-dimensional study

L. J. Carpenter (1) , K. Hebestreit (2) , U. Platt (2) , P. S. Liss (3)

1 Department of Chemistry [York, UK]
2 Institut für Umweltphysik [Heidelberg]
3 School of Environmental Sciences [Norwich]

At Mace Head, Eire, in the coastal East Atlantic, diiodomethane has been identified as an important precursor of iodine oxide radicals. Peak concentrations of both CH₂I₂ and IO at low water indicate that the intertidal region is a strong source of organoiodines. Atmospheric measurements of CH₂I₂ made in marine air are used in conjunction with a 2-dimensional model incorporating horizontal and vertical dispersion to provide estimates of the intertidal and offshore fluxes of CH₂I₂ upwind of Mace Head. The strong signature of photolysis in the CH₂I₂ observations indicates that the emissions are not entirely local/coastal, but must include an additional offshore source. Good agreement between model and measured CH₂I₂ concentrations is achieved with an offshore flux of 2 × 10⁴ molecules cm^-2 s^-1 and an intertidal flux ranging from 1.3 × 10⁹ molecules cm^-2 s^-1 (low water) to 6.5 × 10⁸ molecules cm^-2 s^-1 (high water), the latter over a 100 m wide coastal belt. The coastal emissions at low water are in good agreement with independent estimates made from seaweed emission data. We estimate that, although intertidal emissions are ~4 orders of magnitude higher than those offshore, their contribution to the measured CH₂I₂ concentrations at 10 m height is only ~50%.

Domaines: Océan, Atmosphère

L. J. Carpenter, K. Hebestreit, U. Platt, P. S. Liss. Coastal zone production of IO precursors: A 2-dimensional study. Atmospheric Chemistry and Physics Discussions, 2001, 1 (1), pp.193-220. ⟨hal-00300863⟩