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

[摘要] At Mace Head, Eire, in the coastal East Atlantic, diiodomethane has been identified as animportant precursor of iodine oxide radicals.Peak concentrations of bothCH₂I₂ and IO at low water indicate that the intertidal region is a strong source of organo-iodines.Atmosphericmeasurements of CH₂I₂ made in marine air are compared with the concentrations predicted by a2-dimensional model incorporating horizontal and vertical dispersion of surface emissions. Themodel shows that micrometeorological variability, proximity of the site to emissions, andphotolysis all play important roles in determining the CH₂I₂ concentrations at Mace Head.Inaddition to a tidal-height dependent intertidal flux, which was estimated from seaweed productiondata, a contribution from offshore (non-local) sources was required in order to reproduce thestrong signature of photolysis in the CH₂I₂ observations.A combination of an offshore flux andan intertidal flux (of up to 1.4 × 10⁹ molecules cm^-2s^-1 at low water) results in good agreementbetween the measured and modelled CH₂I₂ concentrations.Although this study does notnecessarily infer emission of CH₂I₂ from the open ocean, it suggests that air-sea exchange ofCH₂I₂ in coastal waters does occur.

[学科分类] 大气科学