The lack of mechanistic knowledge on several aerosol properties and their complex interactions with clouds and radiation hinders the advance in predictive understanding of climatic and environmental impacts of atmospheric aerosol. Single particle morphology and aerosol mixing states are among those aerosol aspects that are the least known and characterized, due to their complexity and inherent measurement challenges. However, these single-particle aspects influence the aerosol optical properties, as well as various microphysical processes like hygroscopicity and heterogeneous ice nucleation. During the aerosol life cycle, particles experience several atmospheric aging processes, such as restructuring, coagulation and condensation with organic and inorganic materials, and heterogeneous chemical reactions. These processes result in changes in morphology and internal mixing state of individual particles. The significance of these effects and, hence, the impact on atmospheric radiation budget, is largely unconstrained and not well understood. New experimental, as well as modeling efforts are needed to better understand the role of aerosol morphology and aerosol mixing state. This session focuses on this timely topic, and we welcome both laboratory and field measurements, as well as modeling efforts that investigate the morphology and mixing of atmospheric particles, their chemical and physical interactions with the environment and their effects, for example, on optical properties and microphysical processes.