In the summer of 1998, an aerosol column closure experiment was conducted over eastern Germany as part of the Lindenberg Aerosol Characterization Experiment (LACE 98). The experimental platforms involved were two aircraft equipped with aerosol in situ instrumentation, an airborne aerosol backscatter lidar and solar irradiance sensors (upwelling and downwelling) to measure optical and microphysical aerosol properties relevant for radiative forcing in the entire atmospheric column from the boundary layer to the tropopause region. Using Mie theory and reasonable assumptions on the particle complex refractive index, the hemispheric backscatter fraction and spectral light scattering coefficients were calculated from the measured aerosol size distribution data. A comparison between optical parameters derived from particle size distribution measurements and optical properties measured by independent techniques yields an uncertainty range of ¿30% for the calculated aerosol optical parameters. Detailed information on the vertical variability of the particle size distribution, the aerosol extinction coefficient and the hemispheric backscatter fraction is given, which is applicable for a realistic representation of aerosol properties in climate models. The estimated daily averaged aerosol shortwave radiative forcing varies from -33 ¿ 12 to -12 ¿ 5 W m-2, and respective aerosol optical depths at λ = 0.710 ¿m range from 0.18 to 0.06.