The refractive index (RI) is a key quantity in calculating many aerosol properties required for climate models. To accurately describe the RI of aerosol, the wavelength and temperature dependence as well as the variation with aerosol water content must be considered. Aside from water, aged ambient aerosol can contain both inorganic salts and a myriad of organic molecules. Determining the optical properties of each organic molecule and their contribution to the aerosol as a whole would be an incredibly time consuming and, in many cases, intractable task. Using single aerosol particle spectroscopy measurements and an effective oscillator model, we are able to measure parameters that can be used to accurately calculate the wavelength-dependent RI of mixed organic-inorganic aqueous aerosol particles. Measured oscillator parameters are presented for a number of atmospherically relevant inorganic ions and surrogate organic species. Finally, the effect of temperature on the oscillator parameters is investigated.