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Ground based measurements of aerosol optical depth, tau, and shortwave irradiance at the Mediterranean island of Lampedusa during 2003 and 2004 were used to estimate the surface aerosol shortwave radiative forcing. The shortwave forcing efficiency (FE) was derived at various solar zenith angles, theta, as the derivative of the shortwave irradiance with respect to tau. Values of FE for different classes of particles, namely desert dust, DD, biomass burning/industrial aerosols, BU, and for the whole dataset are derived. At the summer solstice the daily average FE is -86.4 W/m(2) for DD, -70.5 W/m(2) for BU, and -94.0 W/m(2) for the whole dataset. The daily aerosol forcing of DD is much larger than for the other aerosol classes due to the combination of larger forcing efficiency and largest optical depths. The estimated average daily forcing at the summer solstice and equinox for DD is -30 and -24 W/m(2), respectively.