Ozone deposition to the sea surface: chemical enhancement and wind speed dependence

Deposition of ozone to the sea surface is controlled by complex physical and chemical processes. There is a large variability in the observed deposition velocity of ozone v(d) needed to be better characterized. In addition, the existing formulations for estimating (v(d)) cannot explain a significant ozone loss, particularly, at low wind speed. By amalgamating previous works, a more general formula was developed to account for v(d) dependence on wind speed and chemical enhancement. The result shows that v(d) can be elevated from 0.016 to 0.078 cm s(-1) by about a factor of 5 as wind speed increases from 0 to 20 m s(-1), indicating the importance of wind-induced turbulent gas-transfer. To estimate molecular gas-transfer, represented by the surface reactivity of ozone, reaction rates of species known to react with ozone in seawater were investigated. Iodide was found to be capable of describing the substantial chemical destruction of ozone at low wind speed. Due to a wide range of distribution in the surface oceans (20-400 nM), iodide appears to be a candidate elucidating the variability Of v(d). This study suggests that the physical and chemical processes are coupled and both play significant roles in determining ozone deposition to the sea surface. (C) 2003 Elsevier Ltd. All rights reserved.