DOMINANCE OF MINERAL DUST IN AEROSOL LIGHT-SCATTERING IN THE NORTH-ATLANTIC TRADE WINDS

ATMOSPHERIC aerosols can affect climate by scattering and absorbing so lar radiation(1-3). Most recent studies of such effects have focused l argely on anthropogenic sulphate aerosols, which are believed to exert a substantial cooling influence(2). Mineral dust aerosols have been l argely ignored, because it was thought that their scattering efficienc y and concentrations were too low to have a substantial effect on clim ate. Here we report measurements of the light-scattering properties of North African dust delivered to Barbados by the North Atlantic trade winds. Although the mass scattering efficiency of the dust is only abo ut a quarter of that of non-seasalt sulphate over the North Atlantic(5 ), the annual-mean dust concentration in Barbados trade-wind air is 16 times that of non-seasalt sulphate(6). The net scattering by mineral dust is therefore about four times that by non-seasalt sulphate aeroso ls. African mineral dust should therefore be the dominant lightscatter ing aerosol throughout the tropical and subtropical North Atlantic reg ion, Our observations suggest that mineral dust could be an important climate-forcing agent over this ocean region and in other regions wher e dust concentrations are high(7,8).