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

learn the benefits of using fugacity. This RateConstant model is available from the
Trent University website, but only in DOS format. In principle, the QWASI model
can be applied to any well mixed body of water for which the hydraulic and
particulate flows are defined.
Figure 8.4 shows the transport and transformation processes treated, and Table
8.3 lists the D values and the corresponding fugacity in the rate expressions. Figure
8.5 gives the mass balance equations in steady-state and unsteady-state or differential
form. The steady-state solution describes conditions that will be reached after prolonged
exposure of the lake to constant input conditions, i.e., emissions, air fugacity,
and inflow water fugacity. Also given in Figure 8.5 is the solution to the differential
equations from a defined initial condition, assuming that the input terms remain
constant with time. If it is desired to vary these inputs, or any other terms, as a
function of time, the differential equations must be solved numerically. The subscript
refers to the steady-state solution, which applies at infinite time.
Since D values add, simple inspection reveals which are important and control the
overall chemical fate. For example, if D V greatly exceeds D Q, D C, and D M, it is apparent
that most transfer from air is by absorption. The relative magnitudes of the processes
of removal from water are particularly interesting. These occur in the denominator of
the f W equation as volatilization (D V), reaction (D W), water outflow (D J), particle
outflow (D Y), and a term describing net loss to the sediment. The gross loss to the
sediment is (D D + D T), but only a fraction of this (D S + D B)/(D R + D T + D S + D B) is
Figure 8.4 Transport and transformation processes treated in the QWASI model, consisting
of a defined atmosphere with water and sediment compartments.
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