From NASA's Earth Observatory:
The dust plumes that arose in the western Sahara Desert on January 18, 2012, continued their westward journey the following day. On January 19, 2012, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image of a giant, crescent-shaped plume over the Atlantic Ocean.
North to south, the plume spans several hundred kilometers. Off the coast of Western Sahara, the dust forms a faint crosshatch pattern, which implies that dust particles blow in different directions at different altitudes. Most of the dust blows westward. Saharan dust frequently lands on the Canary Islands and Cape Verde, but also sometimes crosses the Atlantic Ocean to the Americas.