Tar balls (TBs) are a specific particle type which is abundant in the global troposphere, in particular in biomass smoke plumes. These particles belong to the family of atmospheric brown carbon (BrC), which can absorb light in the visible range of the solar spectrum. The refractive index of TBs falls much closer to that of soot than of other light-absorbing species such as humic-like substances. These findings may have substantial influence on the understanding of global radiative energy fluxes.