EFFECT OF BLACK CARBON ON THE OPTICAL-PROPERTIES AND CLIMATE FORCING OF SULFATE AEROSOLS

We study the optical properties of anthropogenic sulfate aerosols cont aining black carbon using a recently developed exact solution of the s cattering problem for a spherical particle (sulfate aerosol) containin g an eccentrically located spherical inclusion (black carbon). We pres ent the expression for the change of planetary albedo due to addition of an absorbing, but optically thin aerosol layer and estimate the eff ect of the black carbon within the sulfate aerosol layer on the aeroso l direct radiative forcing. The black carbon within the sulfate aeroso l reduces the expected sulfate direct cooling effect by about 0.034 W/ m(2) for each 1% of the black carbon to sulfate mass mixing ratio. Thu s the presence of black carbon within sulfate in the background aeroso l does not significantly change the previous estimates of the global a erosol direct cooling effect. However, in regions where the black carb on in sulfate concentrations are of the order of 5% or more, the local and regional effects are significant.