THE EFFECT OF MICROSCALE TURBULENCE ON THE REACTION-RATE IN A CHEMICALLY REACTIVE PLUME

A model of a chemically reactive plume is used to study the effect tha t atmospheric turbulence has on the rate of reaction between NO and O- 3 upon their release into the atmosphere. The model describes only the cycle NO-O-3-NO2 and simulates a release into the atmospheric neutral boundary layer. A Gaussian profile is assumed for the inert species N Ox defined as NOx = NO + NO2. A second-order closure model is used to calculate explicitly concentration (co-) variances of the chemical rea ctive species. The determination of ($) over bar NO'O'(3) is fundament al since it affects the chemical reaction rate during the dispersion p rocess. This has important consequences for the concentration fields o f the reactants and the products. The closure model includes the Damko hler number (the ratio of the time scale of turbulence and the time sc ale of chemistry) of all the species involved in the dispersion/reacti on process. The study of (co-)variances provides insights into the pro cess of dispersion as well as into the influence of turbulence on the chemical reaction rate. The downstream chemistry development clearly s hows the existence of three different phases no reaction, partial reac tion and homogeneous chemistry. The extent of these three phases is de termined by the value of the Damkohler number and the amount of mass r eleased.