The session aims to examine the current state-of-the-science and potential future directions in understanding and describing particle radiative properties, with a specific focus on theoretical, experimental and observational studies of atmospheric particle properties, both aerosols and cloud particles. Radiative properties such as extinction, scattering and absorption coefficients, single scattering albedo, asymmetry factor, and phase function of aerosol and cloud particles in spectral regions from the ultraviolet to microwaves; relevant microphysical properties, like size distributions, refractive index, particle shape and mixture of components. Particle hygroscopicity and effects of relative humidity. Measuring methodologies, both in situ and remote, and temporal and spatial variations of these properties in the Earth's atmosphere are also important topics in this session