In this paper, the influence of a perpendicular structure in front of parallel buildings on the stabilization of pollutants is investigated, taking into account the porous medium. And to test the model, numerical simulation was carried out formulated using the Navier–Stokes governing equations. It is worth noting that attention is paid to configurations with a perpendicularly located box, in the middle of which there is a porous barrier simulating trees. Thus, this allows more realistically reproducing the conditions of the urban environment. The study is based on a test problem reproducing experimental conditions and the use of the RNG k-ε turbulent model. Simulation showed that the presence of perpendicular structures significantly affects the movement of air flows and the distribution of pollutant concentrations. Model adjustments for turbulent viscosity in critical areas were changed with the aim of improving forecast precision of impurity transport. Analysis of the vertical profile of concentrations revealed critical zones where harmful substances accumulate, especially at the level of y/H=1.26. The results were evaluated with experimental data and confirm the reliability of the numerical approach. Also, the distribution of concentration by height changes sharply and at the base of the wall (y/H = 0) it decreases to 0.4, and at y/H =1.26 it reaches a maximum showing a high level of pollution. The obtained results are relevant for the environmental analysis of the urban environment and can be used in planning measures to improve air quality. In the future, it is planned to expand the modeling to more complex urban areas taking into account the relief, multiple sources of pollution and weather conditions, which will improve the accuracy of forecasts and the effectiveness of environmental regulation.