sec-1) and time, t, is measured from the initial expansion time of the plume. Obviously, the initial area and time can be related by Au = (n/2)Kt0. The constituents under study are always taken to be uniformly distributed across the plume. For a chemically active species in a uniform expanding plume, we can estimate the rate of change in the average plume concentration due to expansion as where na is the ambient concentration. Equation 12 presumes that the plume expands by mixing in air containing an ambient abundance of each species, and that mixing within the plume is instantaneous. If K is constant, Eq. 12, by virtue of Eq. 11, becomes The expansion term, Eq. 13, is readily incorporated into the model calculation as a “pseudochemicar' loss process.
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