On the giant sea-salt particles in the atmosphere: I. General Features of the Distribution

Abstract

Some observational data of giant sea-salt particles in the atmosphere, now available from many references, were examined to find mechanisms that would explain their distribution.The first part concerns the vertical distribution over the sea. It is shown that the average decrease of the concentration with height, as a function of particle weight, is quantitatively explained by a combination of sedimentation, diffusion, and convection processes. It is also suggested that the frequent observation of a maximum concentration at some level above the sea surface may be explained by the presence of a boundary layer of a thickness of several meters over the sea surface, where relative humidity steeply changes, in a nonsteady state.In the second part, the distribution over the continent is discussed. The vertical distribution inland is characterized by a low concentration near the ground which may be ascribed mainly to impaction on ground obstacles, an effect which is much greater than dry fallout. This type of distribution is analytically expressed, and some relations have been formulated; for example, the ratio between the maximum and the ground concentrations as related to an efficiency of the impaction by ground obstacles, also the height where the maximum concentrations appear as related to the factor representing the exponential decrease of the concentration with height in an equilibrium distribution at sea. These expressions are used with available data of the actual distribution in order to examine values of the included factors. Transition from the distribution over the sea to that over the continent is also discussed.