VOCs natural convection driven by combined thermal and solutal buoyancy forces in a partially porous cavity has been studied in this paper, including coupled diffusion effects induced by temperature, solute of VOCs and vapor gradients interactions. The mathematical description of the problem is based on a two domain formulation of the conservation equations. FEM was used to solve the partially equations. The paper is focused on the analysis of the characteristic parameters governing diffusive convection: Lewis number and buoyancy forces. The set of numerical results is shown that buoyancy forces induces a specific behavior of the average heat and mass transfer, and Lewis number of VOCs has distinct influence on mass transfer.