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

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Thus, if there is river flow of 1000 m3/h (G) from A to B of water containing 0.3 mol/m3 (C) of chemical, then the corresponding flow of chemical is 300 mol/h (N). Turning to the evaluative environment, it is apparent that the primary candidate advective phases are air and water. If, for example, there was air flow into the 1 square kilometre evaluative environment at 109 m3/h, and the volume of the air in the evaluative environment is 6 ¥ 109 m3, then the residence time will be 6 hours, or 0.25 days. Likewise, the flow of 100 m3/h of water into 70,000 m3 of water results in a residence time of 700 hours, or 29 days. It is easier to remember residence times than flow rates; therefore, we usually set a residence time and from it deduce the corresponding flow rate. Burial of bottom sediments can also be regarded as an advective loss, as can leaching of water from soils to groundwater. Advection of freons from the troposphere to the stratosphere is also of concern in that it contributes to ozone depletion. 6.2.1 Level II Advection Algebra Using Partition Coefficients If we decree that our evaluative environment is at steady state, then air and water inflows must equal outflows; therefore, these inflow rates, designated G m3/h, must also be outflow rates. If the concentrations of chemical in the phase of the evaluative environment is C mol/m3, then the outflow rate will be G C mol/h. This concept is often termed the continuously stirred tank reactor, or CSTR, assumption. The basic concept is that, if a volume of phase, for example air, is well stirred, then, if some of that phase is removed, that air must have a concentration equal to that of the phase as a whole. If chemical is introduced to the phase at a different concentration, it experiences an immediate change in concentration to that of the well mixed, or CSTR, value. The concentration experienced by the chemical then remains constant until the chemical is removed. The key point is that the outflow concentration equals the prevailing concentration. This concept greatly simplifies the algebra of steadystate systems. Essentially, we treat air, water, and other phases as being well mixed CSTRs in which the outflow concentration equals the prevailing concentration. We can now consider an evaluative environment in which there is inflow and outflow of chemical in air and water. It is convenient at this stage to ignore the particles in the water, fish, and aerosols, and assume that the material flowing into the evaluative environment is pure air and pure water. Since the steady-state condition applies, as shown in Figure 6.1a, the inflow and outflow rates are equal, and a mass balance can be assembled. The total influx of chemical is at a rate GACBA in air, and GWCBW in water, these concentrations being the “background” values. There may also be emissions into the evaluative environment at a rate E. The total influx I is thus ©2001 CRC Press LLC I = E + GACBA + GWCBW mol/h Now, the concentrations within the environment adjust instantly to values C A and C W in air and water. Thus, the outflow rates must be G A C A and G W C W . These outflow concentrations could be constrained by equilibrium considerations; for example, they may be related through partition coefficients or through Z values to a common fugacity.
This enables us to conceive of, and define, our first Level II calculation in which we assume equilibrium and steady state to apply, inputs by emission and advection are balanced exactly by advective emissions, and equilibrium exists throughout the evaluative environment. All the phases are behaving like individual CSTRs. Of course, starting with a clean environment and introducing these inflows, it would take the system some time to reach steady-state conditions, as shown in Figure 6.1d. At this stage, we are not concerned with how long it takes to reach a steady state, but only the conditions that ultimately apply at steady state. We can therefore develop the following equations, using partition coefficients and later fugacities. But Therefore, ©2001 CRC Press LLC I = E + GACBA + GWCBW = GACA + GWCW CA = KAWCW I = CW[GAKAW + GW] and CW = I/[GAKAW + GW] Other concentrations, amounts (m), and the total amount (M) can be deduced from CW. The extension to multiple compartment systems is obvious. For example, if soil is included, the concentration in soil will be in equilibrium with both CA and . C W 6.2.2 Level II Advection Algebra Using Fugacity We assume a constant fugacity f to apply within the environment and to the outflowing media, thus, or, in general, I = GAZAf + GWZWf = f(GAZA + GWZW) f = I/(GAZA + GWZW) f = I/ SG Z from which the fugacity and all concentrations and amounts can be deduced. Worked Example 6.1 An evaluative environment consists of 104 m3 air, 100 m3 water, and 1.0 m3 soil. There is air inflow of 1000 m3/h and water inflow of 1 m3/h at respective chemical concentrations of 0.01 mol/m3 and 1 mol/m3. The Z values are air 4 ¥ 10–4, water i i
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McKay, Donald. "Front matter" Multi
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Multimedia Environmental Models The
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hensive, and reliable, and they hav
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Chapter 1 Introduction Chapter 2 So
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McKay, Donald. "Introduction" Multi
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It is now evident that our task is
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McKay, Donald. "Some Basic Concepts
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give the derived units directly wit
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Energy (joule, J) The joule, which
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particles (aerosols), or biota in w
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Worked Example 2.1 A three-phase sy
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(i) What is the concentration (C) i
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Answer ©2001 CRC Press LLC 5.1 kg,
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or or When t is zero, C is zero, th
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What is the absolute minimum piscic
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©2001 CRC Press LLC C 1 = C O/(1 +
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containing nonequilibrium quantitie
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1. Fallout of chemical from air to
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validated using real environments.
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©2001 CRC Press LLC CHAPTER 3 Envi
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of other, somewhat similar or homol
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Table 3.2 List of Chemicals Commonl
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elatively high concentrations. This
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exists between toxicologists and ch
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determine priority. This is a subje
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Another important classification of
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Figure 3.1 (continued) ©2001 CRC P
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Table 3.5 (continued) dichlorometha
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Table 3.5 (continued) total PCB 326
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Figure 3.2 Plot of log K AW vs. log
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chlorofluoro compounds are very sta
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3.3.2.7 Arsenic Compounds Arsenic,
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McKay, Donald. "The Nature of Envir
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Figure 4.1 Evaluative environments.
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are subject to two important deposi
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metals and organic chemicals from w
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carbon figure for deeper sediments
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flows. The quality of this groundwa
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Table 4.2 Evaluative Environments A
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McKay, Donald. "Phase Equilibrium"
Page 81 and 82: Figure 5.1 Some principles and conc
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Page 85 and 86: Another useful quantity is the rati
Page 87 and 88: experimentally, but not directly, u
Page 89 and 90: ©2001 CRC Press LLC 5.3 PROPERTIES
Page 91 and 92: 1.0. This, then, is the fugacity or
Page 93 and 94: where ©2001 CRC Press LLC pH is -l
Page 95 and 96: In terms of solubilities, S iA and
Page 97 and 98: The temperature coefficient is the
Page 99 and 100: (1982), Baum (1997) and Leo (2000).
Page 101 and 102: Although it may appear environmenta
Page 103 and 104: Figure 5.4 Illustration of quantita
Page 105 and 106: 5.5 ENVIRONMENTAL PARTITION COEFFIC
Page 107 and 108: C S = K PC W benzene = 1.1 ¥ 0.001
Page 109 and 110: Mackay (1986), in an attempt to sim
Page 111 and 112: Compartment Definition of Fugacity
Page 113 and 114: high concentration in the fish, but
Page 115 and 116: heat capacity of 0.38 J/g°C requir
Page 117 and 118: Therefore, ©2001 CRC Press LLC f =
Page 119 and 120: ©2001 CRC Press LLC Z T = S(V i/V
Page 121 and 122: ©2001 CRC Press LLC air Z = P S /R
Page 123 and 124: Table 5.1 Table 5.1 Summary of Defi
Page 125 and 126: Figure 5.7 Fugacity form 1 for dedu
Page 127 and 128: Calculate the following physical-ch
Page 129 and 130: ©2001 CRC Press LLC CHAPTER 6 Adve
Page 131: that all water will spend 100 days
Page 135 and 136: ©2001 CRC Press LLC f = 15/0.5 = 3
Page 137 and 138: D AS dominates. A residence time of
Page 139 and 140: and Therefore, ©2001 CRC Press LLC
Page 141 and 142: eaction situation in which there is
Page 143 and 144: The rate constants in each case are
Page 145 and 146: ©2001 CRC Press LLC 1/t O = SD Ai/
Page 147 and 148: e achieved in 10 days. Detractors o
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Page 151 and 152: to Zepp and Cline (1977) for the or
Page 153 and 154: ©2001 CRC Press LLC 6.7 LEVEL II C
Page 155 and 156: Figure 6.3 Fugacity Level II calcul
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Page 159 and 160: Figure 7.1 Illustration of nonequil
Page 161 and 162: 5. Diffusion within soils, and from
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Page 165 and 166: ©2001 CRC Press LLC N = ABDC/ Dy m
Page 167 and 168: no currents or eddies. In practice,
Page 169 and 170: diffusivity, and some unknown layer
Page 171 and 172: where ©2001 CRC Press LLC X = y/ U
Page 173 and 174: fraction of the total volume that i
Page 175 and 176: Figure 7.6 Mass transfer at the int
Page 177 and 178: partition coefficient. The signific
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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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