Distributions of subsonic aircraft emissions are advected as an initial value problem in a 3D transport model to simulate the evolution of emissions in the stratosphere. The sensitivity of transport to season, analyzed tropopause height and aircraft emissions distribution is analyzed. The 1/e-folding lifetime of the emissions of the current fleet is found to be about 50 days, within the range of previous estimates. The lifetime is shorter in January than in July. Within a 90 day period, approximately 7% of emissions in July and 2% in January are lofted into the stratosphere. Pathways for the stratosphere-troposphere exchange of emissions are discussed. ¿ 1998 American Geophysical Union