## Concentration / Setup Run / Deposition Definitions

This section is used to define the deposition parameters for emitted pollutants. The number of deposition definitions must correspond with the number of pollutants released. There is a one-to-one correspondence. There are 5 entries in the CONTROL file for each defined pollutant. The lines 27(1) through 31(5) correspond with each of the menu items shown in the illustration below. The radio-buttons along the top can be used to set default deposition parameters, which can then be edited as required in the text entry section. The second line of radio-buttons define the deposition values for some preconfigured species: Cesium, Iodine, and Tritium. The reset button sets all deposition parameters back to zero.

Note that turning on deposition will result in the removal of mass and the corresponding reduction in air concentration, the deposition will not be available in any output unless height "0" is defined as one of the concentration grid levels.

26 - Number of pollutants depositing

Default: number of pollutants on line # 10

Deposition parameters must be defined for each pollutant species emitted. Each species may behave differently for deposition calculations. Each will be tracked on its own concentration grid. The following five lines are repeated for each pollutant defined. The number here must be identical to the number on line 10. Deposition is turned off for pollutants by an entry of zero in all fields.

27(1)- Particle: Diameter (µm), Density (g/cc), and Shape

Default: 0.0 0.0 0.0

These three entries are used to define the pollutant as a particle for gravitational settling and wet removal calculations. A value of zero in any field will cause the pollutant to be treated as a gas. All three fields must be defined (>0) for particle deposition calculations. However, these values only need to be correct only if gravitational settling or resistance deposition is to be computed by the model. Otherwise a nominal value of 1.0 may be assigned as the default for each entry to define the pollutant as a particle. If a dry deposition velocity is specified as the first entry in the next line (28), then that value is used as the particle settling velocity rather than the value computed from the particle diameter and density.

28(2)- Deposition velocity (m/s), Pollutant molecular weight (Gram/Mole), Surface Reactivity Ratio, Diffusivity Ratio, Effective Henry's Constant

Default: 0.0 0.0 0.0 0.0 0.0

Dry deposition calculations are performed in the lowest model layer based upon the relation that the deposition flux equals the velocity times the ground-level air concentration. This calculation is available for gases and particles. The dry deposition velocity can be set directly for each pollutant by entering a non-zero value in the first field. The velocity can also be calculated by the model using the resistance method which requires setting the remaining four parameters (molecular weight, surface reactivity, diffusivity, and the effective Henry's constant). See the table below for more information.

29(3)- Wet Removal: Actual Henry's constant, In-cloud (L/L), Below-cloud (1/s)

Default: 0.0 0.0 0.0

Suggested: 0.0 3.2E+05 5.0E-05

Henry's constant defines the wet removal process for soluble gases. It is defined only as a first-order process by a non-zero value in the field. Wet removal of particles is defined by non-zero values for the in-cloud and below-cloud parameters. In-cloud removal is defined as a ratio of the pollutant in air (g/liter of air in the cloud layer) to that in rain (g/liter) measured at the ground. Below-cloud removal is defined through a removal time constant.

30(4)- Radioactive decay half-life (days)

Default: 0.0

A non-zero value in this field initiates the decay process of both airborne and deposited pollutants.

31(5)- Pollutant Resuspension (1/m)

Default: 0.0

Suggested :1.0E-06

A non-zero value for the re-suspension factor causes deposited pollutants to be re-emitted based upon soil conditions, wind velocity, and particle type. Pollutant re-suspension requires the definition of a deposition grid, as the pollutant is re-emitted from previously deposited material. Under most circumstances, the deposition should be accumulated on the grid for the entire duration of the simulation. Note that the air concentration and deposition grids may be defined at different temporal and spatial scales.

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