Multimedia fugacity model is a model in

environmental chemistry Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as t ...

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 In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas ...

, which was introduced by

Gilbert N. Lewis Gilbert Newton Lewis (October 23 or October 25, 1875 – March 23, 1946) was an American physical chemist and a Dean of the College of Chemistry at University of California, Berkeley. Lewis was best known for his discovery of the covalent bond ...

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 Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

, 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 The fugacity capacity constant (Z) is used to help describe the concentration of a chemical in a system (usually in mol/m3Pa). Hemond and Hechner-Levy (2000) describe how to utilize the fugacity capacity to calculate the concentration of a chemical ...

expressed as Z-values (SI unit: mol/m³ Pa) for a variety of media, and transport parameters expressed as D-values (SI unit: mol/Pa h) for processes such as

advection In the field of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is a ...

, reaction and intermedia transport. The Z-values are calculated using the equilibrium partitioning coefficients of the chemicals,

Henry's law In physical chemistry, Henry's law is a gas law that states that the amount of dissolved gas in a liquid is directly proportional to its partial pressure above the liquid. The proportionality factor is called Henry's law constant. It was formul ...

constant and other related physical-chemical properties.

Application of models

There are four levels of multimedia fugacity Models applied for prediction of fate and transport of organic chemicals in the multicompartmental environment: Depending on the number of phases and complexity of processes different level models are applied. Many of the models apply to steady-state conditions and can be reformulated to describe time-varying conditions by using differential equations. The concept has been used to assess the relative propensity for chemicals to transform from temperate zones and “condense out” at the polar regions. The multicompartmental approach has been applied to the “quantitative water air sediment interaction" or "QWASI" model designed to assist in understanding chemical fate in lakes. Another application found in POPCYCLING-BALTIC model, which is describing fate of persistent organic pollutants in Baltic region.

Application of models

References

Further reading