Mackay model

Whereas the fugacity approach was used by Mackay for the computation of mass flows and the concentration levels, the SimpleBox adopt the concentration-based piston velocity type mass transfer coefficients (ms-1). This is, mainly, because most scientific papers express the mass transfer in these terms, rather than in terms of the fugacity-based conductivity type coefficients (mol h 1 Pa-1). Furthermore, the transfer and transformation phenomena are treated as simple pseudo first-order processes, similar to Mackay models. 

Figures 10.8a and 10.8b compare the Pp — based J-P and Mackay models to the Koa model, using actual air data from Chicago at 0°C (Harner and Bidleman, 1998b). Kp values were determined from particle phase and gas phase concentrations (equations (1) and (2)) for PCBs, PAHs, and PCNs (polychlorinated naphthalenes) and expressed as particulate fractions, c ), using Equation (9). The model estimates were calculated as described in the example (section 3-5) except that Equation (24) instead of (25) was used for the Koa model, to allow for variation in the organic matter fraction, fom, of the aerosol. In Figure 10.8a, the J-P model overpredicts the particulate fraction, for PCBs but is in good agreement for PAHs. The Mackay model produces somewhat higher values. Another point of interest in...

Comparison of the Junge-Pankow, Mackay, and Koa models for predicting the particulate fraction of POPs in urban air show reasonable agreement, with the Koa model giving somewhat lower and the Mackay model higher results. An unanswered question is does octanol adequately represent the polar and non-polar classes of organic matter on aerosols i.e., is the assumption that yoct and yom are equal valid ... 

Italian monitoring data of freshwater samples related to pesticide contamination in 1997 are reported in Table 7. The pesticides are listed in a decreasing order in respea to Priority Index (P.I.)> an index calculated on the basis of pesticide sold quantity, of the field application rates and of the water repartition evaluated with the Mackay model. In Table 7, the percent of laboratories that searched pesticides (%R) and the percent of positive samples (%P) are also showed. It is evident that the monitoring of some pesticides is very poor, even if they have an elevate P.I. Some active ingredients, like metolachlor and terbuthylazine, are contaminants widespread in freshwaters. 

Several models of varying complexity have been developed to calculate and predict the distribution of chemicals in the environment (OECD, 1989a, 1993c). Most of them are derived from the Mackay model (Mackay 1979 Mackay and Paterson, 1981, 1982, 1990 Mackay, Paterson and Shiu, 1992) to estimate the environmental compartment (air, soil, water and biota) in which the chemical is most likely to be found. Based on the concept of fugac-ity, models were derived for four levels of increasing complexity. Level I... 

Kawamura and MacKay model A model used to represent pool evaporation. 

D. Mackay, Multimedia Environmental Models, Lewis, Chelsea, MI, 1991. 

This equation can be simplified to give H = P/S, where H is now Henry s law constant, which has dimensions of atm mVmole. Values for H may be calculated or measured (Mackay et al. 1979), and are now widely used infugacity modeling (see Section 3.2). 

Multimedia models can describe the distribution of a chemical between environmental compartments in a state of equilibrium. Equilibrium concentrations in different environmental compartments following the release of defined quantities of pollutant may be estimated by using distribution coefficients such as and H s (see Section 3.1). An alternative approach is to use fugacity (f) as a descriptor of chemical quantity (Mackay 1991). Fugacity has been defined as fhe fendency of a chemical to escape from one phase to another, and has the same units as pressure. When a chemical reaches equilibrium in a multimedia system, all phases should have the same fugacity. It is usually linearly related to concentration (C) as follows ... 

Mackay, D. (1991). Multimedia Environmental Models The Eugacity Approach. Chelsea Ml Lewis. 

E. J. Mackay and K. S. Sorbie. Modelling scale inhibitor squeeze treatments in high crossflow horizontal wells. J Can Petrol Technol, 39(10) 47-51, October 1998. 

E. J. Mackay, K. S. Sorbie, M. M. Jordan, A. P. Mathara, and R. Tomlins. Modelling of scale inhibitor treatments in horizontal wells ... 

Diamond ML, Mackay D, Cornett RJ, et al. 1990. A model of the exchange of inorganic chemicals between water and sediments. Environ Sci Technol 24(5) 713-722. 

G Wilson, IF Hassan, CJ Dix, I Williamson, R Shah, M Mackay. Transport and permeability properties of human Caco-2 cells An in vitro model of the intestinal epithelial cell barrier. J Controlled Release 11 25-40, 1990. 

In Mackay s development of an equilibrium model a slice of the earth is selected as a unit world or model ecosystem. Fugac-ities are calculated for each compartment of the ecosystem and the overall distribution patterns of a given chemical are predicted. 

Discussion to this point has presented equilibrium modeling in its simplest form or level I as it is termed by Mackay(2). 

In addition to dissipation of the substance from the model system through degradation, other dissipative mechanisms can be considered. Neely and Mackay(26) and Mackay(3) have also introduced advection (loss of the chemical from the troposphere via diffusion) and sedimentation (loss of the chemical from dynamic regions of the system by movement deep into sedimentation layers). Both of these mechanisms are then assumed to act in the unit world. This approach makes it possible to investigate the behavior of atmosphere emissions where advection can be a significant process. Therefore, from a regulatory standpoint if the emission rate exceeds the advection rate and degradation processes in a system, accumulation of material could be expected. Based on such an analysis reduction of emissions would be called for. 

Neely, W. B. Mackay, D. 1981, presented at workshop "Modeling the Fate of.Chemicals in the Aquatic Environment", Pell-ston, Michigan. 

A very significant advance was made by Baughman and Lassiter (5) when they suggested using evaluative environments for elucidation of the environmental behavior of chemicals. This led to the EXAMS model (6), the studies of selected chemicals by Smith et al (7, 8), the development of "Unit Worlds" by Neely and Mackay (9) and Mackay and Paterson (2), and the incorporation of similar Unit Worlds into hazard assessment by Schmidt-Bleek et al (10). 

Mackay, D. Paterson, S. "Fugacity Models for Predicting the Environmental Behavior of Chemicals", report prepared for Environment Canada 1982. 

Neely, W. B. Mackay, D. "An Evaluative Model for Estimating Environmental Concentrations", in "Modelling the Fate of Chemicals in the Aquatic Environment", editors, Dickson, K.L. Maki, A. W. and Cairns, J., Jr., Ann Arbor Science, Ann Arbor 1982, 127-143. 

Mackay, D. Joy, M. Paterson, S. "AQuantitative Water Air Sediment Interaction (QWASI) Fugacity Model for Describing Chemical Fate in Lakes and Rivers" submitted to Chemosphere, 1983. 

Cowan CE, Mackay D, Feijtel TCJ, van de Meent D, di Guardo A, Davies J, Mackay N (1995) The multi-media fate model a vital tool for predicting the fate of chemicals. SETAC Press, Pensacola... 

Mackay D, Diamond M (1989) Application of the QWASI (quantitative water air sediment interaction) fugacity model to the dynamics of organic and inorganic chemicals in lakes. Chemosphere 18 1343-1365... 

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, Di Guardo A, Paterson S, Kicsi G, Cowan D, Kane D (1996) Assessment of chemical fate in the environment using evaluative, regional and local-scale models illustrative application to chlorobenzene and linear alkylbenzene sulfonates. Environ Toxicol Chem 15(9) 1638-1648... 

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