Clusters: A bridge across the disciplines of environment, materials science, and biology

Abstract

The formation of finite particles and dust grains in interstellar media, heterogeneous reactions occuring in the stratosphere, and unidentified infrared bands in interstellar gas clouds have been suggested to have a cluster origin. In the following, we provide examples where clusters have played a role in describing and accounting for phenomena in atmospheric science. ### Aerosols and Fine Particles. Fine particles are ubiquitous throughout the universe; they are present in interstellar media (e.g., in dense clouds where ion clustering reactions have been invoked in mechanisms responsible for the formation of molecules); they are ultimately responsible for the rings around Saturn; and, in some theories of planetary evolution, they are used to explain the origin of planets themselves. The fascinating issue of interstellar dust, which could serve as a supply of biotic raw material on earth, is also relevant for astrobiology. In high altitudes of our own planet, there are layers of meteoritic ablation where dust layers are known and noctilucent clouds form, possibly enhanced by ion-induced nucleation processes. For more “down-to-earth” reasons, fine particles are of interest to environmental scientists who must contend with them in ways more germane to our everyday life in terms of visibility and health (1–6). Clustering and related nucleation phenomena are, in part, responsible for their formation (7–13). For many years, the community of atmospheric scientists was divided into two groups: those dealing with problems of visibility effects, clouds, and condensation processes and those interested in chemical transformations. Many atmospheric chemists considered heterogeneous processes to be of secondary importance and of third-order interest; they usually attempted to account for most observed phenomena considering only gas-phase reactions. However, one need only realize that gas-phase acid molecules … †To whom correspondence may be addressed. E-mail: pjena{at}vcu.edu or awc{at}psu.edu