Aerosol size distribution in harmattan weather is studied, using a combination of the Yue-Deepak size inversion procedure and the data from photographed aerosol filter samples, for a typical moderate episode in Lagos. Accuracy of retrievals by this method depends sensitively on knowledge of the complex index of refraction of the aerosol. At Lagos, some 1,500 km south of the harmattan dust source, about 57% of the extinction of solar radiation appears due to the particulate mode r>1 μm, a modal extinction less than those obtainable at stations nearer the Sahara. ¿ American Geophysical Union 1988