Advanced / Configuration Setup / Concentration

This section provides some guidance in configuring the model input to perform certain specialized calculations. The default configuration supplied with the test meteorological data is confined to a simple dispersion calculation. More complex scenarios can be configured through the Advanced, Configuration Setup, Concentration menu tab. The menu is used to modify the SETUP.CFG namelist file. This file is not required, and if not present in the root startup directory, default values are used. These parameters can all be changed without recompilation by modification of the contents of SETUP.CFG and in some cases their modification will substantially change the nature of the simulation. The configuration file should be present in the root directory. An illustration of the menu is shown below.

When using the GUI, the namelist file will be deleted and all variables are returned to their default value by selecting the "Reset" button. The following summarizes the namelist variables and their corresponding section in the GUI menu. Not all variables can be set through the menu.

Time Step Selection Criteria

TRATIO (0.75) - defines the fraction of a grid cell that a particle or trajectory is permitted to transit in one advection time step. Reducing this value will reduce the time step and increase computational times. Smaller time steps result in less integration error. Integration errors can be estimated by computing a backward trajectory from the forward trajectory end position and computing the ratio of the distance between that endpoint and the original starting point divided by the total forward and backward trajectory distance.

DELT (0.0) - is used to set the integration time step to a fixed value in minutes from 1 to 60. It should be evenly divisible into 60. The default value of zero causes the program to compute the time step each hour according to the maximum wind speed, meteorological and concentration grid spacing, and the TRATIO parameter. The fixed time step option should only be used when strong winds in regions not relevant to the dispersion simulation (perhaps the upper troposphere) are causing the model to run with small time steps. Improper specification of the time step could cause aliasing errors in advection and underestimation of air concentrations.

Meteorological Sub-grid Size

MGMIN (10) - is the minimum size in grid units of the meteorological sub-grid. The sub-grid is set dynamically during the calculation and depends upon the horizontal distribution of end-points and the wind speed. Larger sub-grids than necessary will slow down the calculation by forcing the processing of meteorological data in regions where no transport or dispersion calculations are being performed. In some situations, such as when the computation is between meteorological data files that have no temporal overlap, the model may try to reload meteorological data with a new sub-grid. This will result in a fatal error. One solution to this error would be to increase the minimum grid size larger than the meteorological grid to force a full-grid data load.

Vertical Grid Coordinate System

KMSL (0) - sets the default for input heights to be relative to the terrain height of the meteorological model. Hence input heights are specified as AGL. Setting this parameter to "1" forces the model to subtract the local terrain height from source input heights before further processing. Hence input heights should be specified as relative to Mean Sea Level (MSL). In concentration simulations, the MSL option also forces the vertical concentration grid heights to be considered relative to mean sea level.

Model Type

INITD (4) - determines if the model is configured as a puff or particle model. Valid options are:

The conversions occur automatically in mixed mode when the horizontal standard deviation of the puff (or particle equivalent) equals the concentration grid size. A use of this approach might be for a long-range or regional puff simulation, where the concentration grid is rather coarse. In this case the puffs may pass between concentration sampling nodes during the initial stages of the transport, a stage when the plume is still narrow. Using mode #104 would start the simulation with particles (and concentration grid cells) and then switch to puff mode (and concentration sampling nodes) when the particles are distributed over a concentration grid cell.

Particle Number

NUMPAR (500) - would be the maximum number of particles or puffs released. NUMPAR has a different meaning for puff and particle simulations. In a full puff simulation (INITD=1,2), only one puff per time step is released, regardless of the value of NUMPAR. In a particle or mixed particle-puff simulation (INITD=0,3,4), NUMPAR represents the total number of particles that are released during one release cycle. Multiple release cycles cannot produce more than MAXPAR number of particles. For a mixed simulation (particle-puff), NUMPAR should be greater than one but does not need to be anything close to what is required for a full 3D particle simulation. In all simulation types, particle or puffs are emitted if the particle count is less than MAXPAR.

MAXPAR (10000) - is the maximum number of particles permitted to be carried at any time during a simulation.

Emission Cycle and Duration

QCYCLE (0.0) - are the number of hours between emission start cycles. A zero value means that the emissions are not cycled. When non-zero, the number of emission hours is repeated again at QCYCLE hours after the starting emission time specified in the input Control file.

KHMAX (9999) - is the maximum age (in hours) that any puff or particle is permitted to attain. All pollutants beyond this age are deleted.

Internal Turbulence Parameterization

ISOT (0) - is a flag used to set the turbulence computational method. The default standard method computes the mixing using a diffusivity approach based upon vertical stability estimates and the horizontal wind field deformation. In shorter-range dispersion simulations (<100 km) the deformation parameterization used in conjunction with larger scale meteorological fields will not reflect the diurnal variations in horizontal turbulence. In this situation it is desirable to use the short-range parameterization in which the turbulent velocities are computed directly from the stability parameters. The input tke (turbulent kinetic energy) option replaces the model's computation of stability with the TKE field from the input meteorological data set. Currently only the ETA forecast model data contain the TKE field. In the variance option, the input data is assumed to contain the 3-dimensional component velocity variance fields. Normally when turbulent fluxes (heat and momentum) are available, they are used to compute stability. The short-range method has an additional option (#2) to force the use of the profile to compute stability, rather than the fluxes. This may be desirable, especially if the fluxes represent averages rather than instantaneous values.

The options available through the menu are highlighted in red. Selection of an option inconsistent with the input meteorological data will result in the calculation using the default parameters.

TKER (0) - is the ratio of the vertical to the horizontal turbulence. A value of zero (the default) uses a TKER value consistent with the turbulence parameterization. A non-zero value forces the vertical and horizontal values derived from the TKE to match the ratio. This option is only valid with ISOT=4 and ISOT=5. Currently this parameter cannot be edited through the GUI.

Puff Dispersion Parameterization

KPUFF (0) - is the flag to use either the linear with time (0) or the square-root with time (1) dispersion equation for the horizontal growth rate of puffs. This parameter does not affect particle dispersion.

Concentration Packing

CPACK (1) - is the flag to turn off (set to 0) concentration output packing. The default is to write the binary concentration file at only those grid points that have a non-zero concentration value (set to 1). Setting the flag to zero results in output of the entire concentration grid. Due to the nature of the packing method, if the plume covers more than 50% of the concentration grid, the default concentration packing will result in larger output file than an unpacked concentration file.

Particle Dump Intervals

PINPF (PARINIT) - default name for the particle dump input file.

NINIT - sets the type of initialization performed. When set to "0" no particle initialization occurs even if the "PINPF" file is found in the root directory. A value of "1" reads the file only during the initialization process. No initialization will occur if the time of the particle dump does not match the time of the model initialization. A value of "2" will check the file each hour during the simulation, and if the times match, the particles will be added to those already contained in the simulation. A value of "3" is similar to the previous case, except the particles in the file replace all the particles in the simulation.

POUTF (PARDUMP) - default name for the particle dump output file.

NDUMP (0) - can be set to dump out all the particle/puff points at selected time intervals to a file called PARDUMP. This file can be read from the root directory at the start of a new simulation to continue the previous calculation. Valid NDUMP settings are [0] for no I/O or [hours] to set the number of hours from the start of the simulation at which all the endpoint positions will be written to the file. The file must exist in the root directory and NDUMP>0 for the model to initialize pollutant particles from the file. NDUMP is used in conjunction with NCYCL (see below).

NCYCL (0)- sets the cycle interval at which the PARDUMP file is to be written after the first write at hours NDUMP. Multiple outputs will overwrite the last output. For instance in a multi-day simulation, one application would be to set NDUMP=24 and NCYCL=24 to output all points at the end of every simulation day. If the model were to crash unexpectedly, the simulation could be restarted from the last PARDUMP output.

Conversion Modules

Changes the model's internal configuration in how it treats the pollutants. Some conversion options require additional modules and specific requirements in setting up the CONTROL file. See the linked discussion under each option for more information.

ICHEM (0) - chemistry module selection index:

Ensemble Configuration Values

Sets the dimensions at which the meteorological grid will be offset for the ensemble calculation. Only one offset (+ or -) in either X, Y, or Z is applied per member.

DXF (1.0) - west to east grid factor for offsetting the meteorological grid in the ensemble calculation.

DYF (1.0) - south to north grid factor for offsetting the meteorological grid in the ensemble calculation

DZF (0.01) - vertical grid factor for ensemble (0.01 ~ 250m)

Variables Not Set in GUI

KSFC (2) - defines the vertical index of the internal meteorological data level that is considered to be the top of the surface layer. This value is used for stability scaling computations. The default index value of 2 is consistent with the default polynomial parameters that results in the height of the surface layer top to default to 75 m AGL.

MAXDIM (1) - is the maximum number of pollutants that can be attached to one particle. Otherwise, if multiple pollutants are defined they are released as individual particles. This feature is only required with chemical conversion modules and is not implemented in the public distribution version.

MAXLVL (35) - are the maximum number of meteorological data levels that can be input to the model. This value exceeds all currently available meteorological data sets.

KRND (6) - at this interval in hours, enhanced puff merging takes place. Enhanced merging is less restrictive and will degrade the accuracy of the simulation. Puffs can be further apart and still be merged into the same position. Less frequent merging will improve accuracy, however too many puffs may remain and the simulation time will be substantially increased. The selection of an appropriate value depends if the pollutant release is instantaneous or continuous. Enhanced merging only occurs when the puff number exceeds 25% of MAXPAR.

FRME (0.10) - is the fraction of the total mass that represents a puff mass at which all puffs with a mass less that puff value will only account for FRME of the total mass. These "Low Mass" puffs will be subject to enhanced merging.

FRMR (0.0) - is the fraction of the mass that is permitted to be removed at KRND intervals. The normal situation is to permit no mass loss. However for certain simulations, such as when a pollutant has a high ambient background relative, a small removal rate will significantly reduce the number of puffs on the grid at no loss in accuracy.

EFILE (null) - file name that contains point-source temporal emission factors, where each record contains the {year month day hour duration latitude longitude emission-rate} of each emission period (including the first one defined in the CONTROL file, in the following format: (I4,2I3,2I5,F6.2,F8.2,F8.0). Note the hour and duration fields should be four characters long (0000), representing hours | minutes.



Table of Contents