Wind blown dust is a major contributor to the tropospheric aerosol mass loading and has a significant effect on the local radiative forcing. Information on aerosol optical properties and their temporal and spatial distribution is very limited. Attempts to derive such information from space, in particular, over land, are in a preliminary stage. Recently, information on aerosol optical properties is becoming available from ground networks within one day from the time the observations are made. In this study, use was made of such real-time aerosol observations, to characterize their optical properties, during a heavy dust event in the sub-Sahel in January 2000. Aerosol optical depths at all wavelengths showed a sharp increase when compared to the average for the season, reaching values up to 3.5 at 500 nm. The Angstrom exponent was reduced from 1.2 to 0.3, and a sharp increase in the single-scattering albedo was found. The aerosol optical properties differed significantly from climatologically available information on dust aerosols, and therefore their timely assimilation into transport models or weather prediction models could be of great relevance. Developments in the ways aerosol are presently observed could influence future treatment of aerosols in climate research. ¿ 2001 American Geophysical Union