A parametrization is needed in global models to account for the sub-grid chemical processes taking place in the plume of an aircraft, since these processes can cause the conversion of a considerable amount of the emitted NOx to reservoir species, such as HNO3. For this purpose, the chemical conversions of nitrogen oxides in the plume of an aircraft were investigated with a newly developed model. The calculated fractions of different nitrogen compounds formed within 24 hours in the exhaust plumes, differentiated for the global domain and season, were used to modify the original aircraft NOx emissions from the ANCAT emission inventory to emissions of various nitrogen compounds and we applied these to the global Chemistry Transport Model KNMI (CTMK). The results obtained imply that neglect of aircraft plume processes in global modeling leads to an overestimation of the NOx and O3 perturbations. Compared with a CTMK calculation with unmodified aircraft NOx emissions, the NOx perturbations in the North Atlantic flight corridor (NAFC) decreased by 15%--55%, due to conversions in the plumes. The resulting O3 perturbation decreased by 15%--25%. ¿ 1997 American Geophysical Union