We developed an in situ measurement system - based on linear Raman spectroscopy - to retrieve quantitative information on polymorphic modifications present in an aerosol. Besides, the Raman spectrum is utilized to determine the gas-phase temperature, which is a key parameter governing crystallinity. The particle polymorphism is obtained from the phonon modes of the particles, while pure rotational Raman spectroscopy is used for gas-phase thermometry. The approach is demonstrated for TiO2 aerosols in air and CO2 with different fractions of its two main polymorphs anatase and ruffle. It forms the basis for future investigations in various gas-to-particle processes.