The number of particles released per cycle NUMPAR (2500) would be the maximum number of particles or puffs released over the duration of the emission. NUMPAR has a different meaning for puff and particle simulations. In a full puff simulation (INITD = 1 or 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.
To simplify certain simulations when a constant particle number release rate is required, specifying a negative value for NUMPAR will over-ride the particle number release rate calculations (in terms of the number of sources, hours emission, and pollutants) and force the particle release rate to be |NUMPAR| particles per hour for each source and pollutant.
The maximum number of particles MAXPAR (10000) is the maximum number permitted to be carried at any time during a simulation. In all simulation types, particle or puffs are only emitted if the particle count is less than MAXPAR. Note that there are situations where NUMPAR can (and should) exceed MAXPAR because the actual particle release rate is computed by dividing NUMPAR by the number of sources, pollutants, and release hours.
The maximum particle duration KHMAX (9999) is the number of hours after release that a particle is dropped from the simulation. For simulations using regional meteorological grids, particles are dropped when the reach the grid boundary. However, when using global meteorological data, it may be computationally prudent to drop particles after they are no longer over the region of interest.