I. Introduction 2
II. Small Ion Generation 2 A. Sources 2 B. Evolution of Small Air Ions 3 C. Ion Equilibrium 4
III. Ion Characterization 6 A. Size 6 B. Mobility 7
IV. Ion Composition 10 A. Chemical Reactions 10 B. Hydration 11
The purpose of this chapter is to provide a general description of the physical and chemical properties of small air ions. An ion is an atom, molecule or cluster, or particle that has lost or gained one or more electrons and has thereby acquired a net electric charge. The term small ion excludes charged particles. In the context of this chapter, a small air ion is a cluster of molecules bound together by the Coulomb force associated with an excess or deficiency of electrons; whereas, a particle maintains its physical integrity regardless of its state of charge. Small air ions are the primary emphasis of this section. The presence of ions in the atmosphere was noticed by Coulomb in 1785.'a Since then, electrical charge in air and other electrical properties of the atmosphere have been investigated almost continuously. A thorough review of the ion literature related to atmospheric electricity is given in the classic volume by Chalmers.'b Research by atmospheric scientists on air ions has continued up to the present. In addition, interest in and research on air ions has been expanded to include such areas as high voltage transmission lines and particulate removal from high technology clean rooms. As indicated in other chapters, there has been considerable effort directed towards investigating possible biological effects of small air ions.