Generic Guidance and Optimum Model Settings for the CALPUFF ...

For long range transport applications > 50km, the CTSG option is not usually considered as
impacts on far-field receptors is of the most interest. In near-field applications involving complex
flows, the grid spacing should usually be sufficiently small enough to resolve both the dominant
and small terrain features adequately.
However, on both near and far field applications, if a terrain feature, such as a mine dump that is
too small to be resolved by the chosen grid cell resolution is expected to directly influence the
plume then the CTSG scheme may be invoked to explicitly detail the flow of plume material
around that terrain obstacle.
3.3 Shoreline Fumigation
Fumigation is classified into two types depending on whether it is a temporal or spatial
phenomenon. The former process, termed “nocturnal inversion breakup fumigation,” occurs when
pollutants from an elevated stack are entrained into the growing convective boundary layer as it
breaks up the nocturnal inversion in the morning. The spatial phenomenon, termed “shoreline
fumigation,” occurs when a thermal internal boundary layer growing with downstream distance
entrains pollutants from an elevated stack near a shoreline. Both phenomena are discussed.
3.3.1 Sub-grid Scale TIBL
The majority of cities in New South Wales are located within a few kilometers of the coastline
such that many sources are affected by complex 3-D flow patterns typical of coastal regions. As
well as sea and land breeze circulation systems, the significant differences between the boundary
layers of marine and overland means distinct changes occur to a dispersing plume moving from
land to sea and vice versa. The CALPUFF modeling system is well suited to handling these
complex phenomena and will do so on a grid by grid cell basis without any invocation by the
modeler as long as CALMET supplies the meteorology to CALPUFF.
Briefly, there are important differences in the structure of the marine and continental boundary
layers which can have significant effects on plume dispersion in the overwater and coastal
environments. The sensible heat flux over the open water is typically more than an order of
magnitude less than that over land. The reasons for this are; water has a higher heat capacity and
is partially transparent to solar radiation resulting in a small diurnal temperature difference; the
sea is more uniform, and, there is a constant supply of moisture in the marine boundary layer. As
a result of these differences the mixing heights overwater are much lower. At the land sea
interface, rapid changes in the dispersion characteristics occur which can significantly affect the
ground-level concentrations from coastal sources. For stacks emitting into the stable zone above
the shallow marine boundary layer, narrow plumes are intercepted by a growing Thermal Internal
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