Marine aerosol concentrations and estimated fluxes over the sea



Aerosol particulate fluxes, generated at the sea surface by the action of the wind, have been derived from a comprehensive series of measurements taken in the Outer Hebrides, off the west coast of Scotland. These observations cover wind speeds from essentially zero to values in excess of 30 m s−1, and show that the particle production, over the radius range from 1 to 25 μm, is very strongly dependent upon the prevailing wind speed, especially for the larger particles. These fluxes, estimated for a height of about 10 m above the ocean surface, may be approximated by an expression comprising the sum of two log-normal distributions (in particle radius R) of the form:

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where the values of fI and R0i remain essentially unchanged with wind speed, but with the values of Ai being strongly dependent upon this parameter.

Alternative formulations of the aerosol flux, based upon combining field observations of the dependence of whitecap coverage upon prevailing wind speed with estimates of aerosol production from laboratory-simulated whitecaps, provide poorer approximations to the aerosol observations, especially at the higher wind speeds when a substantial spume-drop contribution may be expected.