Multimedia fugacity model is a model in environmental chemistry that summarizes the processes controlling chemical behavior in environmental media by developing and applying of mathematical statements or "models" of chemical fate.
Most chemicals have the potential to migrate from the medium to medium. Multimedia fugacity models are utilized to study and predict the behavior of chemicals in different environmental compartments.
The models are formulated using the concept of fugacity, which was introduced by Gilbert N. Lewis in 1901 as a criterion of equilibrium and convenient method of calculating multimedia equilibrium partitioning.
The fugacity of chemicals is a mathematical expression that describes the rates at which chemicals diffuse, or are transported between phases. The transfer rate is proportional to the fugacity difference that exists between the source and destination phases.
For building the model, the initial step is to set up a mass balance equation for each phase in question that includes fugacities, concentrations, fluxes and amounts. The important values are the proportionality constant, called fugacity capacity expressed as Z-values (SI unit: mol/m Pa) for a variety of media, and transport parameters expressed as D-values (SI unit: mol/Pa h) for processes such as advection, reaction and intermedia transport. The Z-values are calculated using the equilibrium partitioning coefficients of the chemicals, Henry's law constant and other related physical-chemical properties.