This article presents an overview of the basic principles of photolysis in the environment from an ecological point of view. Photolysis refers to any chemical process in which a compound is directly or indirectly broken down by light. It may take place wherever light is absorbed by chromo-phores. Photolysis may occur directly by the light-absorbing chromophores or indirectly following the release of reactive species, which are formed via photosensitization. In the terrestrial environment (soil surface, leaf surfaces, or translucent leaves), but particularly in the aquatic habitats these processes are of major ecological significance and subject to many studies. Photolysis is an important determinant of nutrient cycling and trace gas production. In addition to this, photolysis of water is a central process of photosynthesis, but will be considered elsewhere in this encyclopedia.
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