An aircraft plume model has been developed on the basis of two coupled trajectory box models. Two boxes, one for plume and one for background conditions, are coupled by means of a mixing parameterization based on turbulence theory. The model considers comprehensive gas phase chemistry for the tropopause region including acetone, ethane and their oxidation products. Heterogeneous halogen, N<sub>2</sub>O<sub>5</sub> and HO<sub>x</sub> chemistry on various types of background and aircraft-induced aerosols (liquid and ice) is considered, using state-of-the-art solubility dependent uptake coefficients for liquid phase reactions. The microphysical scheme allows for coagulation, gas-diffusive particle growth and evaporation, so that the particle development from 1s after emission to several days can be simulated. Model results are shown, studying emissions into the upper troposphere as well as into the lowermost stratosphere for contrail and non-contrail conditions. We show the microphysical and chemical evolution of spreading plumes and use the concept of mean plume encounter time, <i>t<sub>l</sub></i>, to define effective emission and perturbation indices (<i>EEI</i>s and <i>EPI</i>s) for the North Atlantic Flight Corridor (NAFC) showing <i>EEI</i>(NO<sub>y</sub>) and <i>EPI</i>(O<sub>3</sub>) for various background conditions, such as relative humidity, local time of emission, and seasonal variations. Our results show a high sensitivity of <i>EEI</i> and <i>EPI</i>s on the exact conditions under which emissions take place. The difference of <i>EEI</i>s with and without considering plume processes indicates that these processes cannot be neglected.