The marine iodine cycle has significant impacts on air quality and atmospheric chemistry. Specifically, the reaction of iodide with ozone in the top few micrometres of the surface ocean is an important sink for tropospheric ozone (a pollutant gas) and the dominant source of reactive iodine to the atmosphere. Sea surface iodide parameterisations are now being implemented in air quality models, but these are currently a major source of uncertainty. Relatively little observational data is available to estimate the global surface iodide concentrations, and this data has not hitherto been openly available in a collated, digital form. Here we present all available sea surface (<20 m depth) iodide observations. The dataset includes values digitised from published manuscripts, published and unpublished data supplied directly by the originators, and data obtained from repositories. It contains 1342 data points, and spans latitudes from 70°S to 68°N, representing all major basins. The data may be used to model sea surface iodide concentrations or as a reference for future observations.

Abstract. A fast-response (10 Hz) chemiluminescence detector for ozone (O3) was used to determine O3 fluxes using the eddy covariance technique at the Penlee Point Atmospheric Observatory (PPAO) on the south coast of the UK during April and May 2018. The median O3 flux was −0.132 mg m−2 h−1 (0.018 ppbv m s−1), corresponding to a deposition velocity of 0.037 cm s−1 (interquartile range 0.017–0.065 cm s−1) – similar to the higher values previously reported for open-ocean flux measurements but not as high as some other coastal results. We demonstrate that a typical single flux observation was above the 2σ limit of detection but had considerable uncertainty. The median 2σ uncertainty of deposition velocity was 0.031 cm s−1 for each 20 min period, which reduces with the square root of the sample size. Eddy covariance footprint analysis of the site indicates that the flux footprint was predominantly over water (> 96 %), varying with atmospheric stability and, to a lesser extent, with the tide. At very low wind speeds when the atmosphere was typically unstable, the observed ozone deposition velocity was elevated, most likely because the footprint contracted to include a greater land contribution in these conditions. At moderate to high wind speeds when atmospheric stability was near-neutral, the ozone deposition velocity increased with wind speed and showed a linear dependence with friction velocity. This observed dependence on friction velocity (and therefore also wind speed) is consistent with the predictions from the one-layer model of Fairall et al. (2007), which parameterises the oceanic deposition of ozone from the fundamental conservation equation, accounting for both ocean turbulence and near-surface chemical destruction, while assuming that chemical O3 destruction by iodide is distributed over depth. In contrast to our observations, the deposition velocity predicted by the recently developed two-layer model of Luhar et al. (2018) (which considers iodide reactivity in both layers but with molecular diffusivity dominating over turbulent diffusivity in the first layer) shows no major dependence of deposition velocity on wind speed and underestimates the measured deposition velocities. These results call for further investigation into the mechanisms and control of oceanic O3 deposition.

Abstract. A fast response (10 Hz) chemiluminescence detector for ozone (O3) was used to determine O3 fluxes using the eddy covariance technique at the Penlee Point Atmospheric Observatory on the south coast of the UK during April and May 2018. The median O3 flux was −0.132 mg m−2 h−1 (0.018 ppbv m s−1) corresponding to a deposition velocity of 0.037 cm s−1 (interquartile range 0.017–0.065 cm s−1) – similar to the higher values previously reported for open ocean flux measurements, but not as high as some other coastal results. Eddy covariance footprint analysis of the site indicates that the flux footprint was predominantly over water (> 96 %), varying slightly with tide. At moderate-to-high wind speeds, ozone deposition increased with wind speed, and showed a linear dependence with friction velocity of comparable magnitude to predictions from the one-layer model of (Fairall et al., 2007). Deposition was also elevated at very low wind speeds, most likely because the footprint contracted to include a greater land contribution in these conditions.

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Response to Referees' Comments We thank the referee for their comprehensive and constructive comments on our manuscript. Below, we address each specific point in turn:This paper describes coastal ozone flux measurements made at a location on the south coast of the UK. The paper builds on previous techniques to process & understand the data including its uncertainty. The paper includes a comparison of the data to estimates from oceanic ozone deposition models. The way that the paper is written most benefits readers who are very familiar with oceanic ozone deposition measurements and models. I would urge the authors to make changes in order to expand the read-C1