A Lagrangian stochastic (single particle) model is modified in order to account for simple chemistry reactions and tested against measured wind tunnel data. These data refers to a reactive plume generated by a single point source of NO inside a turbulent grid flow doped with ozone. The comparisons were made at different distances from the emission considering all the substances involved in the experiment. The cross correlation terms between the concentrations of the different chemical compounds are neglected or parameterised. Despite this simplification the results are rather satisfactory and seem to encourage practical applications in real atmosphere.