PHOTO 18 Refinery capacity is an important factor in gasoline prices. However, such facilities are also sources of petroleum spills and atmospheric releases of volatile organic compounds that can play a role in local air quality. In the United States most refineries are located near marine transportation terminals along the Gulf of Mexico and the northeastern Atlantic seaboard. (Photo courtesy of Environmental Research Consulting.)

lution in the hydrosphere, deposition in the lithosphere, volatilization into the atmosphere, and ingestion by organisms in the biosphere. Physical processes degrading oil include evaporation, emulsification, and dissolution, whereas chemical processes focus on photooxidation and biological processes emphasize microbial oxidation.

The transportation of oil in the marine environment occurs in two directions, horizontal and vertical. Horizontal transport involves spreading and surface advection, leading in some instances to shoreline stranding and tarball formation. Transport in the vertical direction includes dispersion, entrainment, Langmuir circulation, sinking, overwashing, and sedimentation. Consideration is also given to oil in icy conditions and oil released in deep water.

Conceptual models can be developed to build deterministic models for specific oil loadings for specific sources. The development and distribution of composite fate models, up to now, focus largely on surface oil slicks.

Oil entering the marine environment comes from natural sources (oil seeps) and from sources over which humankind has some control (oil spills, urban runoff, pollution resulting from oil transportation and production, and oil usage in ve