Measurements of direct solar radiation at two window wavelengths were performed with a portable Volz sun-photometer (type III) during the scientific cruise from the Mediterranean to the Indian Ocean on the vessel Salernum (January and February 1979). From these data, evaluations of Angstr¿m's parameters were obtained, describing the atmospheric turbidity conditions associated with the aerosol particle populations in the maritime areas of the Red Sea, Indian Ocean, and Somalian coast. The spectral exponent α was found to range mostly between 0.2 and 0.7 in coastal areas and between 0.3 and 0.9 in the ocean. The parameter β mostly varies from 0.10 to 0.35 in coastal areas and from 0.05 to 0.25 in the oceanic ones. Estimates of the vertical mass loading M of particulate matter were obtained by examining the particulate optical thicknesses in terms of extinction models based on realistic bimodal size distributions of particles. Relatively low values of M were found in the area of Bitter Lakes and Suez Gulf. The quantity M was found to increase gradually in the Red Sea, as the vessel was moving southward, and to reach rather high values around 80 μg cm-2 in the leg along the Somalian coast. In the ocean, M was found to range around 25 μg cm-2 for the most part owing the sea salt component.