ABSTRACT
This chapter describes the major mechanisms of photochemical transformations, rate equations and predictive models for the reactions, the chemistry of reactive inorganic intermediates in natural waters, and the importance of these processes in controlling the aquatic fate of natural and synthetic organic compounds. Photochemical transformations in aquatic systems are not limited to dissolved substances; studies have shown that oxide particles that act as semiconductors photocatalyze reactions of organic compounds adsorbed to their surfaces. Humans are concerned primarily with terrestrial primary production because it provides most of their food and all their natural fiber and wood. Chemists are able to derive simulation models for only a few fairly simple indirect photochemical processes occurring in natural waters. The principal difference between the rate equations for photolysis and rate expressions for thermal reactions is the dependency of the former on the rate of light absorption.
