The AER two-dimensional chemistry-transport model is used to study the effect on stratospheric ozone (O3) from operations of supersonic and subsonic aircraft. The study is based on six emission scenarios provided to AER. The study showed that: (1) the O3 response is dominated by the portion of the emitted nitrogen compounds that is entrained in the stratosphere; (2) the entrainment is a sensitive function of the altitude at which the material is injected; (3) the O3 removal efficiency of the emitted material depends on the concentrations of trace gases in the background atmosphere; and (4) evaluation of the impact of fleet operations in the future atmosphere must take into account the expected changes in trace gas concentrations from other activities. Areas for model improvements in future studies are also discussed. Ko, Malcolm K. W. and Weisenstein, Debra K. and Sze, Nein Dak and Rodriguez, Jose M. and Heisey, Curtis Unspecified Center ATMOSPHERIC CHEMISTRY; ENVIRONMENT EFFECTS; EXHAUST EMISSION; MATHEMATICAL MODELS; OZONE DEPLETION; POLLUTION TRANSPORT; ATMOSPHERIC COMPOSITION; COMBUSTION PRODUCTS; EXHAUST GASES; STRATOSPHERE; TRACE ELEMENTS; TWO DIMENSIONAL MODELS...