The flow rates of DPM particles and gas that are initially supplied to any 2D case are assumed to correspond with those that would apply if the model were 1m deep. Massflows can be scaled by changing the Depth under Boundary Conditions >Reference Values. Changing the depth will scale the massflows internally, so that the reported quantities correspond to the new scaled massflow.
EXAMPLE: If an equal mass of particles and fluid (each with densities set to 1000 kg/m^3) are injected. If I start with Depth set to 1m, a volume integral monitor of DPM concentration might show 64 kg. If I then change the reference depth to 0.5 m, and restart the run the volume integral monitor immediately drops to 32 kg. In each case, the DPM mass matches the mass of injected gas that I get from doing a volume integral of Density. The area average concentrations of DPM particles stay the same, however.