A regional climate model is used to evaluate dry deposition of ozone over the North East Atlantic. Results are presented for a deposition scheme accounting for turbulent and chemical enhancement of oceanic ozone deposition and a second non-chemical, parameterised gaseous dry deposition scheme. The first deposition scheme was constrained to account for sea-surface ozone-iodide reactions and the sensitivity of modelled ozone concentrations to oceanic iodide concentration was investigated. Simulations were also performed using nominal reaction rate derived from in-situ ozone deposition measurements and using a preliminary representation of organic chemistry. Results show insensitivity of ambient ozone concentrations modelled by the chemical-enhanced scheme to oceanic iodide concentrations, and iodide reactions alone cannot account for observed deposition velocities. Consequently, we suggest a missing chemical sink due to reactions of ozone with organic matter at the air-sea interface. Ozone loss rates are estimated to be in the range of 0.5–6？ppb per day. A potentially significant ozone-driven flux of iodine to the atmosphere is estimated to be in the range of 2.5–500？M molec ？？ , leading to a mixing-layer enhancement of organo-iodine concentrations of 0.1–22.0？ppt, with an average increase in the N.E. Atlantic of around 4？ppt per day. 1. Introduction Ozone plays a key role in atmospheric chemistry, absorbing harmful UV rays in the stratosphere whilst simultaneously acting as a greenhouse gas (radiative forcing of tropospheric ozone is around 25% that of CO2 [1]), and acting as a harmful pollutant in the troposphere [2–4]. Influencing the oxidising capacity of the atmosphere as a powerful oxidising agent, it is the dominant precursor to the ubiquitous hydroxyl radical which acts as an atmospheric cleansing agent by determining the lifetime of important atmospheric trace gases. It is vital, therefore, that tropospheric ozone concentrations are realistically simulated in modelling both air pollution and chemistry-climate interactions. 600–1000？Tg？O3 year-1 is removed from the troposphere via dry deposition [5]. The deposition of ozone to water surfaces is small compared to deposition to land [6]: typically, the rate of dry deposition of ozone to the continent is nearly six times faster than the dry deposition rate of ozone to the ocean [7]. However, considering 70% of the globe has ocean coverage, the loss of marine boundary layer ozone via oceanic dry deposition still represents a significant sink for the global ozone budget. Obtaining an accurate
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