Uptake of methanol to the North Atlantic Ocean surface

An anticorrelation between atmospheric methanol (CH(3)OH) concentrations and wind speed and a positive correlation between dimethylsulphide (DMS) concentrations and wind speed have been observed at the coastal air monitoring site of Mace Head in Ireland, during a period of cyclonic activity in which the averaged surface wind speed changed substantially as a low-pressure system evolved over the northeast Atlantic. These observations suggest a net air-to-sea flux of CH(3)OH. This conclusion is supported by the good agreement between the wind speed dependencies of the measured gas concentrations and theoretical predictions using wind-induced turbulent gas transfer velocities of DMS and CH(3)OH calculated from a resistance model, embedded in a photochemical box model. For a wind speed of 8 m s(-1), an ocean deposition rate of methanol of between 0.02 and 0.33 cm s(-1) is calculated, with a best estimate of 0.09 cm s(-1), in good agreement with deposition rates used in global models and derived from atmospheric budgets. The large uncertainty in the calculated deposition rates is due almost entirely to the uncertainty in the degree of saturation of methanol in the surface ocean, highlighting the critical requirement for measurements of methanol in seawater. Owing to the dependence on wind speed, the deposition rates calculated showed substantial range and the calculated contribution of ocean deposition to total loss of CH(3)OH (ocean uptake and gas phase OH oxidation) varied from approximately 20% to 60%.