Microorganisms (i.e. bacteria, archaea, fungi, and protists) as well as viruses and macromolecules are ubiquitous in the atmosphere. They originate from surfaces including terrestrial, aquatic, marine, cryospheric, and built environments, and redistribute across large spatial and temporal scales. The continuous exchange of biological material by atmospheric transport provides an important but still poorly understood link between distant ecosystems and habitats. Once airborne, microbial cells are exposed to temperature fluctuations, radiation, oxidants, and limited availability of water and nutrients. These conditions can affect their survival, biological functioning, potential infectivity and virulence, as well as their physical characteristics, with important implications for microbial and viral dispersal, gene flow, and for the ability of microorganisms to establish and spread in new environments.

Microorganisms, viruses, and microbially-produced macromolecules can also influence atmospheric and Earth-system processes. Biological particles and macromolecules can act as cloud condensation nuclei (CCN) and ice-nucleating particles (INP), affecting cloud formation, precipitation, and potentially the climate. Microbial activity may also affect atmospheric chemical budgets and biogeochemical cycles. Finally, dry and wet deposition returns airborne microorganisms, viruses, and macromolecules to soils, vegetation, water, and ice impacting microbial distribution across these environments. Thus, the atmosphere is as an important interface connecting microbial communities and biogeochemical cycles across ecosystems.

This session aims to bring together researchers from microbiology, atmospheric science, biogeochemistry, climate science, One Health, and related disciplines to advance our understanding of atmospheric microorganisms, their interaction with the atmosphere, and their various effects. We welcome contributions addressing (I) microbial survival, activity, and interactions; (II) atmospheric stress responses and microbial evolution; (III) airborne pathogens, infectivity, virulence, and antimicrobial resistance; (IV) emission, transport, transformation, and deposition; (V) biological ice-nucleating particles and cloud–microbe interactions; (VI) microbial contributions to atmospheric chemistry and biogeochemical cycling; and (VII) the consequences of atmospheric microorganisms and viruses for ecosystems, agriculture, climate, and human and animal health.