The previous example showed a snapshot of the particle
or puff center positions after 12 hours. Air concentrations are
computed by summing each particle’s mass as it passes over the
concentration grid. In the particle model mode, the concentration
grid is treated as a matrix of cells, each with a volume defined
by the grid dimensions. Therefore the concentration is just the
particle mass divided by the cell volume.
3D Particle: ΔC = q(Δx Δy Δz)^{1}
TopHat: ΔC = q(Π r^{2} Δz)^{1}
Guassian: ΔC = q(2Π σ_{h}^{2} Δz)^{1} e^{ 0.5x2/σh2}
In the puff calculation, the concentration grid
is considered as a matrix of sampling points, such that the puff
only contributes to the concentration as it passes over the sampling
point. In the puff calculation mode it is possible for a puff
to pass between points and not be shown on the display.
TopHat: ΔC = q(Π r^{2} Δz_{p})^{1}
Guassian: ΔC = q(2Π σ_{h}^{2} Δz_{p})^{1} e^{ 0.5x2/σh2}
Shown below are the concentration patterns associated with the
particle (left) and puff (right) distributions from the previous
example. Note that the puff distribution is smoother but also
initially somewhat broader. In this particular
case, the horizontal puff growth equations give larger values than
the particle expansion. The noisy particle distribution indicates that more
particles than 5000 are needed to better represent the horizontal distribution.
Particle Concentrations 
TopHat Puff Concentrations

