Approximated boundary conditions of the equation of diffusion

The paper focuses on boundary conditions in mathematical physics equations. These equations describe the processes of pollutants' migration. The emphasis is put on the influence of boundary conditions' approximation on the solution of one-dimensional advection-dispersion equation. Analytical and numerical solutions were used as a basis for the theoretical consideration. The research included the following methods: `distant boundary' method, rejection of diffusion flux in the boundary profile, rejection of `the near field' and solution of mass or energy balance equation. The research afforded possibilities for quantitative and qualitative identification of the influence of boundary conditions' approximation methods on the equation solution inside domain. The derived formulas made it possible to estimate the margin of error introduced by the simplified method. The formulas were presented in the form of nomograms.