Abstract :
The influence of the turbulent fluctuations of concentrations on nonlinear chemical reactions can be treated in an exact manner using the probability density function (p.d.f.) approach. A Monte Carlo simulation yielding the joint p.d.f. of reactive species was implemented in order to investigate the effect of small-scale nonhomogeneity on chemical reactions in the surface layer. First, comparisons of predictions with experimental data from, respectively, a turbulent reactive plume and a heated turbulent boundary layer showed that the method is reliable for addressing environmental model problems. Second, a model pollution situation was scrutinized, namely, the dispersion and chemical reaction of a pollutant released from a ground source into the atmospheric boundary layer. The numerical simulation provided detailed information regarding the effect of small-scale nonhomogenity. Especially, the intensity of segregation was analyzed and it was subsequently demonstrated that fine-scale fluctuations of concentrations resulting from nonhomogeneity strongly limit the mean reaction rate. The influence of both emission flux and Damköhler number was systematically studied; it was found that increasing one of these parameters strengthens the effect of small-scale nonhomogeneity on the chemical process.
