Dispersion Model Configuration

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    HIGHLIGHTS
  • Defining dispersion pollutants
  • Concentration grid definition

The control file (CONTROL) for dispersion simulations is configured from the Concentration / Concentration Setup menu tab.  The concentration setup layout is identical to the trajectory menu with the exception of an additional button to set the emissions, deposition, and concentration grid.

The Pollutant, Deposition and Grids setup button will bring up a submenu with each of the three main options (Pollutant, Grids, Deposition). The pollutant emission rate and deposition must be set for each pollutant.  Normally simulations are run for one pollutant. Several independent concentration grids may be defined for each simulation. However, they may be nested in space or time if desired.  Concentrations for each pollutant species are output on all grid(s).

An arbitrary 4-character field identifies each pollutant.  The emission rate is mass units per hour. The actual mass unit is not specified, so for instance, if the units are kg, then concentration output will be in kg/m3.  Any unit is acceptable, however some chemical conversion modules require specific units.  The emission start time can be set to any time at or after the start of the simulation.  As is true for all time units, zero’s default to the simulation start time in the main menu.  Zero for the month and non-zero values for day and hour cause those values to be treated as relative to the simulation start time.

Each concentration grid must be defined.  Zeros for the grid center default to the source location.  The grid spacing is especially important in concentration computations in determining the cell size (particles) or sampling resolution (puffs).  When multiple levels are defined, each height represents the top of the cell (particles) or actual height (puffs).  The averaging time starts at the sampling start time.  Snapshot (now) concentrations are the average over one time step at the time interval specified and maximum will save the maximum concentration at each grid point over the duration of the output interval.


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