Multimedia fugacity models

The current version of CalTOX (CalTOX4) is an eight-compartment regional and dynamic multimedia fugacity model. CalTOX comprises a multimedia transport and transformation model, multi-pathway exposure scenario models, and add-ins to quantify and evaluate variability and uncertainty. To conduct the sensitivity and uncertainty analyses, all input parameter values are given as distributions, described in terms of mean values and a coefficient of variation, instead of point estimates or plausible upper values. 

LEV3EPI Level in multimedia fugacity model predicts partitioning of chemicals among air, soil, sediment, and water under steady-state conditions for a default model "environment"... 

Besides the fugacity models, the environmental science literature reports the use of models based on Markov chain principle to evaluate the environmental fate of chemicals in multimedia environment. Markov chain is a random process, and its theory lies in using transition matrix to describe the transition of a substance among different states [39,40]. If the substance has all together n different kinds of states,... 

Mackay D, Paterson S (1991) Evaluating the multimedia fate of organic chemicals a level III fugacity model. Environ Sci Technol 25 427-436... 

Mackay D (1991) Multimedia environmental models the fugacity approach. Lewis Publishers, Chelsea... 

Mackay D (2001) Multimedia environmental models - the fugacity approach, 2nd edn. CRC Press/Taylor Francis Group, Boca Raton... 

While QWASI is an easy to use multimedia fate modeling tool, it has been originally designed as a fugacity model. Even though an adaptation to ionic substances exists and it has been applied to lead before, it needs to be recognized that it does not take speciation of metals into account. This adds to the overall uncertainty of results. 

Lohmann U, Roeckner E (1996) Design and performance of a new cloud microphysics scheme developed for the ECHAM4 general circulation model. Clim Dyn 12 557-572 Mackay D (1991) Multimedia Environmental Models The Fugacity Approach. Lewis Publishers, Chelsea, MI, USA... 

In the multimedia models used in this series of volumes, an air-water partition coefficient KAW or Henry s law constant (H) is required and is calculated from the ratio of the pure substance vapor pressure and aqueous solubility. This method is widely used for hydrophobic chemicals but is inappropriate for water-miscible chemicals for which no solubility can be measured. Examples are the lower alcohols, acids, amines and ketones. There are reported calculated or pseudo-solubilities that have been derived from QSPR correlations with molecular descriptors for alcohols, aldehydes and amines (by Leahy 1986 Kamlet et al. 1987, 1988 and Nirmalakhandan and Speece 1988a,b). The obvious option is to input the H or KAW directly. If the chemical s activity coefficient y in water is known, then H can be estimated as vwyP[>where vw is the molar volume of water and Pf is the liquid vapor pressure. Since H can be regarded as P[IC[, where Cjs is the solubility, it is apparent that (l/vwy) is a pseudo-solubility. Correlations and measurements of y are available in the physical-chemical literature. For example, if y is 5.0, the pseudo-solubility is 11100 mol/m3 since the molar volume of water vw is 18 x 10-6 m3/mol or 18 cm3/mol. Chemicals with y less than about 20 are usually miscible in water. If the liquid vapor pressure in this case is 1000 Pa, H will be 1000/11100 or 0.090 Pa m3/mol and KAW will be H/RT or 3.6 x 10 5 at 25°C. Alternatively, if H or KAW is known, C[ can be calculated. It is possible to apply existing models to hydrophilic chemicals if this pseudo-solubility is calculated from the activity coefficient or from a known H (i.e., Cjs, P[/H or P[ or KAW RT). This approach is used here. In the fugacity model illustrations all pseudo-solubilities are so designated and should not be regarded as real, experimentally accessible quantities. 

Mackay, D. (2001) Multimedia Environmental Models The Fugacity Approach. 2nd edition, Lewis Publishers, CRC Press, Boca Raton, FL. 

Mention has already been made of mathematical models which simulate partitioning in the environment. This has been facilitated by the introduction of fugacity principles to environmental modelling, which simplifies the linking of complex partition and rate constants in many of the current multimedia environmental models. A detailed explanation of the ideas involved, and their application, has recently been published by Mackay.39... 

D. Mackay, Multimedia Environmental Models-The Fugacity Approach, Lewis, 1991. 

The multimedia urban model (MUM) is a fugacity-based mass balance model that treats the movement of POPs in an urban environment and links emissions to ambient chemical concentrations, and thus outdoor exposure (Diamond et al., 2001). MUM considers longterm, average conditions of chemical transport and transformation among six environmental compartments in urban areas (air, soil, surface water, sediment, vegetation and surface film see Figure 6.1) shows a concepmal version of the model). The model does not estimate event-specihc processes as do meteorological-based air or stormwater models. 

Mackay, D. (1991) Multimedia Environmental Models the Fugacity Approach, Ujwis, Chelsea, MI. 

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