Pollutants emitted from industrial stacks can be transformed by chemical re
actions. An interesting case is the NO to NO2 conversion due to reactions w
ith the ambient ozone. A simple and practical model has been developed to c
alculate this conversion in the vicinity of the source. Spatial distributio
ns of the reactive species concentrations in the plume are represented by g
eneralized Gaussian profiles. The influence of non-linear chemistry is take
n into account by means of different dispersion parameters for each species
. The model itself consists of a limited number of ordinary differential eq
uations which are easy to solve numerically. The wind tunnel reactive plume
experiment of Builtjes has been simulated. Comparison between the results
of this simple model and calculations involving the complete partial differ
ential equations solved on a refined mesh shows that this generalized Gauss
ian representation of the transverse profiles is valid except very near the
source. It turns out that the influence of chemistry on the dispersion par
ameters has to be taken into account in order to predict the NO/NO2 convers
ion accurately.