Dominance of mineral dust in aerosol light-scattering in the North Atlantic trade winds

ATMOSPHERIC aerosols can affect climate by scattering and absorbing solar radiation^1-3. Most recent studies of such effects have focused largely on anthropogenic sulphate aerosols, which are believed to exert a substantial cooling influence². Mineral dust aerosols have been largely ignored, because it was thought that their scattering efficiency and concentrations were too low to have a substantial effect on climate. 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 about a quarter of that of non-seasalt sulphate over the North Atlantic⁵, the annual-mean dust concentration in Barbados trade-wind air is 16 times that of non-seasalt sulphate⁶. The net scattering by mineral dust is therefore about four times that by non-seasalt sulphate aerosols. African mineral dust should therefore be the dominant light-scattering aerosol throughout the tropical and subtropical North Atlantic region. Our observations suggest that mineral dust could be an important climate-forcing agent over this ocean region and in other regions where dust concentrations are high^7,8.