Reactive below-cloud scavenging is simulated using general chemical re
action simulation. Modelling of mass transfer is mathematically equiva
lent to modelling of chemical reactions. The computer model is flexibl
e as regards input of chemical reactions and transport of species, whi
ch means that changes in the components, reactions, and transport of s
pecies can be made without reprogramming. The numbers of species, reac
tions, and compartments between which mass transfer takes place may be
large and they are only limited by computing time and memory capacity
. The set-up of the matrix equation necessary for general simulation o
f chemical reactions and transport of species is applied for scavengin
g of a NH3 plume.