A new physical analogy for the discrete approximation of the vertical diffusion equation is presented. It is based on the resistor-capacitor chain and incorporates the classical resistance approach to dry deposition simulation in a natural way. It is shown that in the simplest case the finite chain of resistors and capacitors is equivalent to a second-order discrete representation of the diffusion equation resulting from the K theory closure. However, the scheme provides several features, which either cannot be obtained from straightforward discretization at all, or would require a sophisticated construction for their justification and realization. The examples discussed include a thick model layer with a highly variable vertical diffusion coefficient and an internal emission source, interaction with a chemical transformation unit, and spectral features of the model's vertical structure.