Renewed interest in the potential impact of stratospheric aircraft on atmospheric ozone has focused on emissions of nitrogen oxides (NOx). This work shows that enhancement of the sulfate aerosol layer by aircraft emissions of sulfur could be more significant to the ozone impact than emission of NOx, especially when emissions of NOx in future engines are reduced by a factor of three from present engine designs. Our calculations show that increases in the aerosol surface area of the stratosphere by factors of two to three are expected if significant amounts of aircraft-emitted sulfur are converted to sulfuric acid and undergo homogeneous nucleation in the aircraft plume. This possibility is supported by both in situ stratospheric observations and plume/wake modeling. ¿ American Geophysical Union 1996