When localized near high atmospheric pollutant emission sources, living areas can be im- pacted by high pollutant concentrations. This is particularly the case when a highway crosses a densely built area such as a city. In order to limit pollutant concentrations in these sensitive areas, local structures can be built. Noise-barriers, frequently found along roadside near cities, is an exemple of these structures. Built with the aim of reducing noises generated by the road trafic, they also act by reducing pollutant concentrations by modifying the local dispersion of pollutants. Effects of noise-barriers were studied in situ with 3D computational fluid dynamics simulations. Results show that noise-barriers can induce flow patterns such as street-canyon patterns which can radicaly modify the dispersion of trafic related pollutants. In the streamwise direction, pollutant concentrations observed after the barriers can decrease to reach less than 30% of the maximal concentration observed at roadside. These results are obtanied for a given road width and noise-barriers height, and could probably change for other lengths.