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

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Figure 8.11 Transport and transformation processes in a typical activated sludge plant represented as three well mixed compartments. The relative chemical fluxes, e.g. (100), are illustrative. 8.11.1 Introduction ©2001 CRC Press LLC 8.11 INDOOR AIR MODELS We present here a very simple model of chemical fate in indoor air. Numerous studies have shown that humans are exposed to much higher concentrations of certain chemicals indoors than outdoors. Notable are radon, CO, CO 2, formaldehyde, pesticides, and volatile solvents present in glues, paints, and a variety of consumer products. The key issue is that, whereas advective flow rates are large outdoors, they are constrained to much smaller values indoors. Attempts to reduce heating costs often result in reduced air exchange, leading to increased chemical “entrapment.” A nuclear submarine or a space vehicle is an extreme example of reduced advection. Fairly complicated models of chemical emission, sorption, reaction, and exhaust in multichamber buildings have been compiled [e.g., Nazaroff and Cass (1986, 1989) and Thompson et al. (1986)], but we treat here only the simple model developed by Mackay and Paterson (1983), which shows how D values can be used to estimate indoor concentrations caused by evaporating pools or spills of chemicals. An example of the effective use of fugacity for compiling mass balances indoors is the INPEST model, developed in Japan by Matoba et al. (1995, 1998). This model successfully describes the changing concentration of pyrethroid pesticides applied indoors in the hours and days following their application. Because of the reduced advection, there is a potential for high concentrations and exposures immediately following pesticide use, and it may be desirable to evacuate the room or building for a number of hours to allow the initial peak concentration in air to dissipate. The INPEST fugacity model, which is in the form of a spreadsheet, can be used to suggest effective strategies for avoiding excessive exposure. It can be used to compare pesticides and explore the effects of different application practices.
8.11.2 Model of a Chemical Evaporating Indoors We treat a situation in which a pool of chemical is evaporating into the basement air space of a two-room (basement plus ground level) building with air circulation. If the building were entirely sealed and the chemical were nonreactive, evaporation would continue until the fugacity throughout the entire building equalled that of the pool (f P). Of course, it is possible that the pool would have been completely evaporated by that time. The evaporation rate can be characterized by a D value D 1 corresponding to kAZ, the product of the mass transfer coefficient, pool area, and air phase Z value. If the chemical were in solution, it would be necessary to invoke liquid and gas phase D values in series, i.e., the two-film theory as discussed in Chapter 7. The evaporated chemical may then be advected from one room to another with a D value D 2 defined as GZ, the product of the air flow or exchange rate and the air phase Z value. From this second room, it may be advected to the outdoors with another D value D 3. These advection rates are normally characterized as “air changes per hour” or ACH, which is the advection rate G divided by the room or building volume and is the reciprocal of the air residence time. Typical ACHs for houses range from 0.25 to 1.5 per hour. The outdoor air has a defined background fugacity f A. It is apparent that the chemical experiences three D values in series in its journey from spill to outdoors, thus the total D value will be given by ©2001 CRC Press LLC 1/D T = 1/D 1 + 1/D 2 + 1/D 3 and the flux N is D T(f P – f A) mol/h. Of interest are the intermediate fugacities in the rooms, which can be estimated from the equations. N = D 1(f P – f 1) = D 2(f 1 – f 2) = D 3(f 2 – f A) This is essentially a “three-film” or “three-resistance” model. Degrading reactions could be included, leading to more complex, but still manageable, equations. Sorption to walls and floors could also be treated, but it is probably necessary to include these processes as differential equations. Worked Example 8.3 An example of a “spill” of a small quantity (1 g) of PCB over 0.01 m 2 (e.g., from a fluorescent ballast) was considered by Mackay and Paterson (1983). The PCB fugacity was 0.12 Pa and the outdoor concentration was taken as 4 ng/m 3 or 3.7 ¥ 10 –8 Pa. The three D values (expressed as reciprocals) are 1/D 1 = 49000, 1/D 2 = 30, 1/D 3 = 15 Thus, D T is essentially D 1, most resistance lying in the slow evaporation process from the small spill area. The molar mass is 260 g/mol, and the evaporation rate N is then
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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"
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Figure 5.1 Some principles and conc
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likely using an equilibrium criteri
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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
Page 183 and 184: Figure 7.8 Movement of air phase (k
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Page 187 and 188: Figure 7.9 Combination of D values
Page 189 and 190: Figure 7.10 Four-compartment Level
Page 191 and 192: Table 7.2 Order of Magnitude Values
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Page 195 and 196: Figure 7.12 Sample Level III output
Page 197 and 198: McKay, Donald. "Applications of Fug
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Page 201 and 202: Another approach is to employ Monte
Page 203 and 204: LEVEL1B A six-compartment Level I p
Page 205 and 206: Figure 8.1 Air-water exchange proce
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Page 209 and 210: Figure 8.2 Chemical transport and t
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Page 213 and 214: 8.5.2 Process Description The water
Page 215 and 216: learn the benefits of using fugacit
Page 217 and 218: where Figure 8.5 QWASI model: stead
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Page 221 and 222: C F ª Z Ff W ª 1.608 mol/m 3 ª 4
Page 223 and 224: y Mackay et al. (1983), and an appl
Page 225 and 226: accordingly, but the final solution
Page 227 and 228: Figure 8.10 Fish bioaccumulation pr
Page 229 and 230: The nature of the processes control
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Page 233: An alternative and more elegant met
Page 237 and 238: Paterson et al. (1991), and Hung an
Page 239 and 240: 8.14.1 Introduction ©2001 CRC Pres
Page 241 and 242: mated again in mg/day. Food, the ot
Page 243 and 244: models. Most interest is in LRT in
Page 245 and 246: available from the University of To
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