Keywords: air pollutant dispersion, finite element method, second-order closure model
Study of turbulence and pollutant dispersion in a neutrally and unstably stratified atmosphere using a second-order closure boundary-layer model
A one-dimensional, mesoscale second-order closure boundary-layer model is developed to simulate wind flow in a horizontally homogeneous atmosphere. The velocity, potential temperature and turbulent kinetic energy are calculated prognostically, while other second-order moments are modelled diagnostically. The calculated turbulence is then treated as background turbulence to model the dispersion of pollutants emitted from a hypothetical continuous point source. The dispersion model is of second-order closure that prognostically calculates both the mean and second-order moments. Numerical simulations of turbulence and pollutant dispersion in a neutrally and unstably stratified atmosphere are performed. The calculated velocity fluctuation profiles and pollutant concentrations agree well with experimental measurements. The calculated pollutant concentrations in neutral stability show Gaussian plume shape. However, their unstable counterparts show obvious plume descent and rise that is non-Gaussian in nature. This study demonstrates the capability of second-order closure models in calculating plume dispersion in neutral and unstable stratification.