It's an ill wind
"The dust falls in such quantities as to dirty everything on board, and to hurt people's eyes; vessels even have run on shore owing to the obscurity of the atmosphere. It has often fallen on ships when several hundred miles from the coast of Africa, and at points 1,600 miles distant in a north and south direction." Charles Darwin's note from 1832 suggests the dust clouds that engulfed HMS Beagle as it anchored in St Jago in the Cape de Verd Islands off the African coast were dramatic, if unsettling. But they were by no means freak events. Such clouds - which can be as large as the Spanish mainland - form all year round, as dust is whipped up from the continent's arid savannahs and carried across the north Atlantic to the Caribbean and beyond. The dust blowing off Africa contributes most of some 2bn tonnes' worth shunted around the atmosphere each year (the rest originating in Asia, South America, the US and Australia). But while those immediately downwind of the clouds know well the mayhem they can cause, new research is revealing a hitherto unforeseen danger the dust clouds may pose.