Please refer to
Technical Memorandum ERL ARL-224
for a complete review of
equations used to compute air concentrations. However, briefly ...
The default model simulation as configured on the web (within READY)
assumes a horizontal puff distribution and vertical particle dispersion.
The horizontal resolution of the concentration grid is defined based on the
run duration as chosen by the user (ranging from 0.01 to 0.20). As puffs
pass over the concentration grid nodes (grid intersection points) the
puff's air concentration (mass divided by puff area) is summed at that
node. Summation continues over the duration of the concentration
averaging time. Because particle dispersion is assumed in the vertical,
any puffs that fall within the predefined concentration layers (value set by
the user) are the only ones that contribute to the node summation. Final
air concentration is obtained by dividing the sum by the layer depth.
Model input defines the source term as Mass units per hour. Air
concentration output becomes mass units per cubic meter. If your mass
unit is Bq then output concentrations are Bq/m^3. Mass units are
arbitrary and user defined.
Roland Draxler