Dust in the Caribbean atmosphere traced to an African dust storm

Previous aerosol studies have shown that large quantities of dust are often present in the trade winds entering the Caribbean area; indirect evidence suggested that this material was derived from arid regions in Africa. We report here on a dust event which we observed at Barbados on June 12, 1967, and which we have traced to a dust storm covering a large area of West Africa on June 7, 1967; the storm is clearly visible in an ESSA 5 satellite photograph. The composition of the dust from this storm is similar to that of dusts collected during the summer and fall at Barbados except that the particle size distribution of the storm-derived dust is skewed sharply toward the larger particles: 25% of the sample mass consists of particles above 10 μm diameter and 4% above 20 μm diameter; we attribute the anomalous character of the size distribution to the unusually energetic nature of the dust storm. On the basis of similarities in composition and air parcel trajectories, we conclude that most of the airborne dust transported over the western Atlantic Ocean during the summer and early fall is derived from the same general area of the storm — Spanish Sahara, Mauritania, Mali and Senegal.

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