The wavelength-dependence of the complex refractive indices (RI) in the visible spectral range of secondary organic aerosols (SOA) and of biomass burning aerosol, and the evolution of the RI with atmospheric aging are largely unknown. In this study, we apply a novel white light-broadband cavity enhanced spectroscopy to measure the changes in the RI (365−650 nm) of biogenic and anthropogenic SOA produced and aged in an oxidation flow reactor, simulating daytime aging under different NOx concentrations. In addition, we use novel new tar balls proxies to study the effect of atmospheric aging on the optical properties of biomass burning aerosols. Correlating the observed optical properties with aerosol mass spectrometer measurements allows to correlate changes in the chemical composition of the aerosols and their optical properties. Comparison with field samples will be presented.