Atmospheric aerosol plays an important role in the global climate system by contributing to radiative forcing in many ways. Albedo is strongly dependent on light scattering and absorption by aerosol. Both properties can considerably be changed by physical and chemical processing - especially of the organic aerosol formed from oxidation and halogenation of atmospheric trace gases. The enhanced formation of secondary organic aerosol (SOA) from various organic precursors and its subsequent processing by artificially injected molecular halogens was investigated in comparison with naturally released halogens in atmospheric simulation chambers. A major outcome of this research is that halogen species significantly change the size distribution of the SOA, the presence of functional groups and the optical properties - with consequences for the albedo. Furthermore, they even form halogenated species in the condensed (solid or liquid) phase.