The goal of this study is to assess the performance of an innovative Lattice Boltzmann (LB) - Large Eddy Simulation (LES) approach in simulating neutral and stratified pollutant dispersion in complex urban environments. Different simulations are performed for the central area of Paris, accounting for continuous neutral or non-neutral gas releases from a circular source located in both channeled or confined flows. Predicted concentrations are compared with detailed wind tunnel measurements from the MODITIC project (FFI, 2016). Results exhibit a good qualitative and quantitative agreement between numerical and experimental data for the different configurations studied. All the estimated quality metrics match acceptance criteria. In addition, it is shown that the new LBM LES approach is able to capture and highlight the key turbulent mechanisms underlying dispersion process in and above urban areas. Hence, being based on extensive and detailed simulations and quality assurance studies, this paper highlights that the developed approach is well suited to address urban dispersion issues, including accidental chemical releases and short term exposure problems. Such results are particularly valuable to support the design and use of fast response dispersion models.