Probability density function modelling of concentration in and above a canopy layer

Non-linear chemical reactions and other important processes depend on average concentration as well as on the fluctuations of concentration of chemical species. Probability density function (PDF) modelling is a powerful tool for evaluating in an exact manner chemical reaction depending on higher order concentration moments. However, only few studies are devoted to investigate applications of PDF modelling to pollutant dispersion and reactions in atmospheric turbulence. In real cases, very often the emissions/reactions of pollutants take place in and above a canopy layer (urban canopy, vegetation canopy); therefore, the vertical turbulence inhomogeneity plays a relevant role. This inhomogeneity can be efficiently taken into account by PDF approach. We implement a simplified one-dimensional model for the velocity composition PDF by coupling a Monte Carlo simulation and a micro-mixing model (IECM). Under a general assumption of horizontally homogeneous extensive plane source the proposed model is able to fairly reproduce all the concentration moments measured in a laboratory experiment on scalar dispersion within a model plant canopy.