McKay, Donald. "Front matter" Multimedia Environmental Models ...

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Thus, the larger (faster) rate constant dominates. The characteristic times t F and t R (i.e., 1/k F and 1/k R) combine as reciprocals to give the total time t T, as do electrical resistances in parallel, i.e., ©2001 CRC Press LLC 1/t F + 1/t R = 1/t T = k T + k R Thus, the smaller (shorter) t dominates. The term t R can be viewed as a reaction persistence. Characteristic times such as t R and t F are conceptually easy to grasp and are very convenient quantities to deduce when interpreting the relative importance of environmental processes. For example, if t F is 30 years and t R is 3 years, t T is 2.73 years; thus, reaction dominates the chemical’s fate. Ten out of every 11 molecules react, and only one leaves the lake by flow. 2.9 REAL AND EVALUATIVE ENVIRONMENTS The environmental scientist who is attempting to describe the behavior of a pesticide in a system such as a lake soon discovers that real lakes are very complex. Considerable effort is required to measure, analyze, and describe the lake, with the result that little energy (or research money) remains with which to describe the behavior of the pesticide. This is an annoying problem, because it diverts attention from the pesticide (which is important) to the condition of the lake (which may be relatively unimportant). A related problem also arises when a new chemical is being considered. Into which lake should it be placed (hypothetically) for evaluation? A significant advance in environmental science was made in 1978, when Baughman and Lassiter (1978) proposed that chemicals may be assessed in “evaluative environments” that have fictitious but realistic properties such as volume, composition, and temperature. Evaluative environments can be decreed to consist of a few homogeneous phases of specified dimensions with constant temperature and composition. Essentially, the environmental scientist designs a “world” to desired specifications, then explores mathematically the likely behavior of chemicals in that world. No claim is made that the evaluative world is identical to any real environment, although broad similarities in chemical behavior are expected. There are good precedents for this approach. In 1824, Carnot devised an evaluative steam engine, now termed the Carnot cycle, which leads to a satisfying explanation of entropy and the second law of thermodynamics. The kinetic theory of gases uses an evaluative assumption of gas molecule behavior. The principal advantage of evaluative environments is that they act as an intellectual stepping stone when tackling the difficult task of describing both chemical behavior and an environment. The task is simplified by sidestepping the effort needed to describe a real environment. The disadvantage is that results of evaluative environment calculations cannot be validated directly, so they are suspect and possibly quite wrong. Some validation can be sought by making the evaluative environment similar to a simple real environment, such as a small pond or a laboratory microcosm. Later, we construct evaluative environments or “unit worlds” and use them to explore the likely behavior of chemicals. In doing so, we use equations that can be
validated using real environments. A somewhat different assembly of equations proves to be convenient for real environments, but the underlying principles are the same. ©2001 CRC Press LLC 2.10 SUMMARY In this chapter, we have introduced the system of units and dimensions. A view of the environment has been presented as an assembly of phases or compartments that are (we hope) mostly homogeneous rather than heterogeneous in properties, and that vary greatly in volume and composition. We can define these phases or parts of them as “envelopes” about which we can write mass, mole, and, if necessary, energy balance equations. Steady-state conditions will yield algebraic equations, and unsteady-state conditions will yield differential equations. These equations may contain terms for discharges, flow (diffusive and nondiffusive) of material between phases, and for reaction or formation of a chemical. We have discriminated between equilibrium and steady state and introduced the concepts of residence time and persistence. Finally, the use of both real and evaluative environments has been suggested. Having established these basic concepts, or working tools, our next task is to develop the capability of quantifying the rates of the various flow, transport, and reaction processes.
Page 1 and 2: McKay, Donald. "Front matter" Multi
Page 3 and 4: Multimedia Environmental Models The
Page 5 and 6: hensive, and reliable, and they hav
Page 7 and 8: Chapter 1 Introduction Chapter 2 So
Page 9 and 10: McKay, Donald. "Introduction" Multi
Page 11 and 12: It is now evident that our task is
Page 13 and 14: McKay, Donald. "Some Basic Concepts
Page 15 and 16: give the derived units directly wit
Page 17 and 18: Energy (joule, J) The joule, which
Page 19 and 20: particles (aerosols), or biota in w
Page 21 and 22: Worked Example 2.1 A three-phase sy
Page 23 and 24: (i) What is the concentration (C) i
Page 25 and 26: Answer ©2001 CRC Press LLC 5.1 kg,
Page 27 and 28: or or When t is zero, C is zero, th
Page 29 and 30: What is the absolute minimum piscic
Page 31 and 32: ©2001 CRC Press LLC C 1 = C O/(1 +
Page 33 and 34: containing nonequilibrium quantitie
Page 35: 1. Fallout of chemical from air to
Page 39 and 40: ©2001 CRC Press LLC CHAPTER 3 Envi
Page 41 and 42: of other, somewhat similar or homol
Page 43 and 44: Table 3.2 List of Chemicals Commonl
Page 45 and 46: elatively high concentrations. This
Page 47 and 48: exists between toxicologists and ch
Page 49 and 50: determine priority. This is a subje
Page 51 and 52: Another important classification of
Page 53 and 54: Figure 3.1 (continued) ©2001 CRC P
Page 55 and 56: Table 3.5 (continued) dichlorometha
Page 57 and 58: Table 3.5 (continued) total PCB 326
Page 59 and 60: Figure 3.2 Plot of log K AW vs. log
Page 61 and 62: chlorofluoro compounds are very sta
Page 63 and 64: 3.3.2.7 Arsenic Compounds Arsenic,
Page 65 and 66: McKay, Donald. "The Nature of Envir
Page 67 and 68: Figure 4.1 Evaluative environments.
Page 69 and 70: are subject to two important deposi
Page 71 and 72: metals and organic chemicals from w
Page 73 and 74: carbon figure for deeper sediments
Page 75 and 76: flows. The quality of this groundwa
Page 77 and 78: Table 4.2 Evaluative Environments A
Page 79 and 80: McKay, Donald. "Phase Equilibrium"
Page 81 and 82: Figure 5.1 Some principles and conc
Page 83 and 84: likely using an equilibrium criteri
Page 85 and 86: Another useful quantity is the rati
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experimentally, but not directly, u
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©2001 CRC Press LLC 5.3 PROPERTIES
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1.0. This, then, is the fugacity or
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where ©2001 CRC Press LLC pH is -l
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In terms of solubilities, S iA and
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The temperature coefficient is the
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(1982), Baum (1997) and Leo (2000).
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Although it may appear environmenta
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Figure 5.4 Illustration of quantita
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5.5 ENVIRONMENTAL PARTITION COEFFIC
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C S = K PC W benzene = 1.1 ¥ 0.001
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Mackay (1986), in an attempt to sim
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Compartment Definition of Fugacity
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high concentration in the fish, but
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heat capacity of 0.38 J/g°C requir
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Therefore, ©2001 CRC Press LLC f =
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©2001 CRC Press LLC Z T = S(V i/V
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©2001 CRC Press LLC air Z = P S /R
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Table 5.1 Table 5.1 Summary of Defi
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Figure 5.7 Fugacity form 1 for dedu
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Calculate the following physical-ch
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©2001 CRC Press LLC CHAPTER 6 Adve
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that all water will spend 100 days
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This enables us to conceive of, and
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©2001 CRC Press LLC f = 15/0.5 = 3
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D AS dominates. A residence time of
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and Therefore, ©2001 CRC Press LLC
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eaction situation in which there is
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The rate constants in each case are
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©2001 CRC Press LLC 1/t O = SD Ai/
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e achieved in 10 days. Detractors o
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sulfate to sulfide or by dechlorina
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to Zepp and Cline (1977) for the or
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©2001 CRC Press LLC 6.7 LEVEL II C
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Figure 6.3 Fugacity Level II calcul
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McKay, Donald. "Intermedia Transpor
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Figure 7.1 Illustration of nonequil
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5. Diffusion within soils, and from
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sionally, the term flux rate is use
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©2001 CRC Press LLC N = ABDC/ Dy m
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no currents or eddies. In practice,
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diffusivity, and some unknown layer
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where ©2001 CRC Press LLC X = y/ U
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fraction of the total volume that i
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Figure 7.6 Mass transfer at the int
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partition coefficient. The signific
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and the series retains a similar ra
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ments of resuspension rates are par
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Figure 7.8 Movement of air phase (k
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ates can thus be used to estimate m
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Figure 7.9 Combination of D values
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Figure 7.10 Four-compartment Level
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Table 7.2 Order of Magnitude Values
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Unlike the Level II calculation, it
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Figure 7.12 Sample Level III output
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McKay, Donald. "Applications of Fug
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applications. Citations are given t
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Another approach is to employ Monte
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LEVEL1B A six-compartment Level I p
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Figure 8.1 Air-water exchange proce
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The total rates of transfer are thu
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Figure 8.2 Chemical transport and t
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mean. For chemical between depths o
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8.5.2 Process Description The water
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learn the benefits of using fugacit
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where Figure 8.5 QWASI model: stead
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are similar to those described by M
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C F ª Z Ff W ª 1.608 mol/m 3 ª 4
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y Mackay et al. (1983), and an appl
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accordingly, but the final solution
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Figure 8.10 Fish bioaccumulation pr
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The nature of the processes control
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iomagnification is more significant
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An alternative and more elegant met
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8.11.2 Model of a Chemical Evaporat
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Paterson et al. (1991), and Hung an
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8.14.1 Introduction ©2001 CRC Pres
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mated again in mg/day. Food, the ot
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models. Most interest is in LRT in
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available from the University of To
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McKay, Donald. "Appendix" Multimedi
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©2001 CRC Press LLC
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