ABSTRACT
Pollutants are capable of movement over considerable distances. They can be carried over boundaries between countries, thereby raising political as well as environmental problems, because even the unintended export of environmental chemicals tends not to be welcomed by countries that receive them. Scandinavian countries, for example, have objected to the deposition of aerially transported sulfur dioxide (SO2) originating from the British Isles. For the most part, transport over large distances is a consequence of the mass movement of air or water. However, movement may also be by diffusion that may be rapid in air but less rapid in water. Movement by diffusion may be localized or spread over large distances especially in air.
