Multiphase chemistry deals with chemical reactions, transport processes, and transformations between gaseous, liquid, and solid matter. After deposition, viable bioparticles can trigger and other particles can interfere with metabolic activity and biological reproduction or disease. These effects may stimulate or suppress further emissions, thus closing a biogeochemical cycle and related feedback loops in the Earth system. The multiphase processes involved in the cycling of gases, aerosols, clouds, and precipitation are important for the evolution, current state, and future development of the atmosphere and climate as well as the biosphere and public health. Aerosol particles are ubiquitous in the atmosphere and affect climate by scattering or absorption of light and serving as nuclei for cloud droplets, ice crystals, and precipitation.