Thorsten Hohaus and his colleagues from the IEK-8 at the FZ-Jülich are developing a new continuous stirred-tank reactor SAPHIR-STAR in order to study the formation and chemical composition of atmospheric aerosols and their gas phase precursors under different atmospheric conditions and oxidation regimes. Within the aeroHEALTH project SAPHIR-STAR will be employed to investigate the role of the chemical composition of atmospheric aerosols on their potential toxicity.