Large Eddy Simulation of the Mixing Process of Gaseous Pollutants Using a Lagrangian Stochastic Model

The mixing process of reacting gaseous pollutants in a turbulent flow is essential to understand the formation of resultant aerosols. Unfortunately, this issue is only rarely investigated. In this study, a large eddy simulation (LES) model is combined with a Lagrangian stochastic model to explore the mixing process of two gaseous pollutants in an atmospheric turbulent boundary layer. Simulation results show that the atmospheric turbulences drive the pollutant parcels to form obvious spatial structures, and the mass concentration exhibits an inhomogeneous distribution. The growth and dissipation rate of the mixing zone sizes both show approximately linear behaviors, and the variation rate of the latter is almost twice of the former. Surprisingly, the distance between two emission sources generally does not affect the formation and dissipation time of the mixing zone with the same mass concentration. The mean volume of mixing zone with a certain mass concentration decreases linearly with distance of two emission sources under the same wind condition, while it decreases exponentially with increasing free stream velocity if the distance of two sources is fixed. Thus, the increasing wind velocity can reduce the mixing zone more effectively compared with that of inter-sources distance. From this study, a critical distance between two emission sources and their emission strategies can be suggested if the wind condition is known. This research can also provide an effective way to determine an optimized siting of various emission sources.