## Advanced / Configuration Setup / Release Particles or Puffs

The menu is divided into two sections. In each case the value of the INITD namelist parameter is being set. In the upper portion of the menu, the model is configured as either a full 3D particle or puff model, or some hybrid combination of the two. The released particles or puffs maintain their mode for the entire duration of the simulation. Valid options are:

- 0 - 3D particle horizontal and vertical (DEFAULT)
- 1 - Gaussian-horizontal and Top-Hat vertical puff (Gh-THv)
- 2 - Top-Hat-horizontal and vertical puff (THh-THv)
- 3 - Gaussian-horizontal puff and vertical particle distribution (Gh-Pv)
- 4 - Top-Hat-horizontal puff and vertical particle distribution (THh-Pv)

Introduced with the September 2004 version are mixed mode model calculations, where the mode can change during transport depending upon the age (from release) of the particle. A mixed-mode may be selected to take advantage of the more accurate representation of the 3D particle approach near the source and the smoother horizontal distribution provided by one of the hybrid puff approaches at the longer transport distances. In a long-range or regional puff simulation, where the concentration grid may be rather coarse, 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 multiple concentration grid cells. Valid options are:

- 103 - 3D particle (#0) converts to Gh-Pv (#3)
- 104 - 3D particle (#0) converts to THh-Pv (#4)
- 130 - Gh-Pv (#3) converts to 3D particle (#0)
- 140 - THh-Pv (#4) converts to 3D particle (#0)
- 109 - 3D particle converts to grid (global model)

A new option (109) introduced with the January 2009 version (4.9), converts 3D particles to the Global Eulerian Model grid. The particles are transferred to the global grid after the specified number of hours. This approach should only be used for very long-range (hemispheric) transport due to the artificial diffusion introduced when converting pollutant plumes to a gridded advection-diffusion computational approach. The method is ideal for estimating contributions to background concentrations. All mixed- mode particles/puffs (not just 3D) will convert to the global grid if the global option is selected from the special runs menu.

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