A study of the aerosol in different marine environments was performed during a scientific cruise on the vessel Salerrnurn from the Mediterranean Sea to the Indian Ocean (January 1 to February 27, 1979). The aerosol particles were sampled on membrane filters and in a single-stage impactor. The particles on the filters were analyzed for soluble Mg, Ca, K, Na; for mineral aerosol mass concentration; and for chloride particles. An elemental analysis, using the microprobe attached to the scanning electron microscope (SEM), was carried out. The aerosol particle size distribution was determined from the photographs of the filter surface taken by the SEM. The concentration of the ice-forming nuclei was measured by developing the filters in a static diffusion chamber. Chloride particles were also independently detected on the single-stage impactor slides. The data, also discussed in association with the atmospheric turbidity measurements taken during the same cruise, give a clear picture of the aerosol characteristics, which reflect in a detailed and sensitive way the origin of the air mass in which they were sampled. few observations have been made in environments undisturbed by human activity, such as the Southern Hemisphere, and the open oceans and wide continental areas of the Northern Hemisphere. Moreover, since the few data available mostly refer to total aerosol mass concentration, they are of little use for studying the effects of aerosol on cloud microphysics and radiation or for understanding basic processes such as the transfer of particulate matter from seawater to air, the long-range transport of the continental component, or the relative contribution of the different sources to the background aerosol. The vessel Salemum was scheduled to sail to the Indian Ocean to perform radiosonde launchings as a part of the Global Atmospheric Research Program (GARP); space onboard was made available to research teams, and the opportunity was taken to perform samplings and observations in order to contribute to a better knowledge of the geographic climatology of aerosols in areas where few measurements have been performed. In fact the only data previously available were obtained by Sadasivan [1978] in the Arabian Sea, at latitudes greater than 20øN, and by Prospero [1979] in the Bengali Gulf. The region is of particular interest, considering the great importance of the Sahara desert as a source of mineral dust which is transported over great distances. Outbreaks of Sahara dust ober the North Atlantic Ocean have been investigated by several authors [Jaenicke and Schutz, 1978; Prospero and Carlson, 1972; Carlson and Prospero, 1972, among others], whereas Sahara dust transport eastward, though apparent from satellite observations, has been studied much less. Furthermore, the opportunity to spend a relatively long sampling period at latitude 0 ø in order to investigate aerosol characteristics in the Intertropical Convergence Zone (ITCZ) was considered of interest. This paper presents the results of the analysis of several seri...