An inverted optical tweezers system has been used to trap single component organic aerosol droplets. The hygroscopic properties of these aerosols were investigated using whispering gallery modes in their Raman spectra to accurately elucidate droplet sizes and refractive indices at different relative humidities (RH). We focus on organic compounds with O/C=1, to ascertain whether a relationship between hygroscopicity and O/C exists. Hygroscopicity data were analysed with the hygroscopicity parameter (kappa) model, and a more rigorous κ-Köhler growth factor model.
