Well, i don’t understand how. So do you mean to say that i don't need to parallelize this UDF?

Particle termination happens when the mass deposited is less than 0.00005*massInjected.

And as far as the scalar update goes this is how i update the mass deposited C_UDMI(c,t,Mass_Dep)+=(InjectedMass-PenetratedMass). 

PenetratedMass = InjectedMass*Efficiency

that still does not explain the difference in volume integral.