The transport of exhaust effluents and the possibility of water ice contrail formation are investigated under the specific fluid dynamical conditions in the near exhaust trail of a subsonic jet aircraft at cruise altitude. By means of a computational model describing the two-dimensional turbulent mixing of a single jet of hot exhaust gas with the atmosphere, representative results are discussed on the temperature and saturation ratio evolutions of air parcels in the jet flow field as well as on radial distributions of exhaust effluents undergoing chemical reactions behind the nozzle exit with prescribed, typical net reaction rates. The results underline the importance of a simultaneous treatment of spatially resolved jet expansion together with microphysical and chemical processes, because this coupling leads to distinct concentration patterns for various classes of chemical reactants and is essential for the detailed prediction of contrails. ¿ American Geophysical Union 1994