Abstract. A box and a Gaussian plume model including gas-phase photochemistry and with plume dispersion parameters estimated from the few available plume observations are proposed and used for evaluation of photochemical transformations of exhausts from a single subsonic transport aircraft. The effects of concentration inhomogeneities in the plume cross section on the photochemical sources and sinks in the plume are analyzed for various groups of compounds. The influence of these inhomogeneities on the rate and on the mass of ambient air entrainment into the plume are studied also by comparing the box and the Gaussian plume model simulations during the first hours of their "life''. Due to the enterance of HO_x and NO_x from ambient air into the plume with rates varying from the wind shear and turbulence conditions, the rate of emitted NO_x oxidation in the plume is dependent on these and also on the background concentration levels of HO_x and NO_x.