We investigate the potential contribution of organic species emitted by aircraft engines to the formation of ultrafine volatile particles detected in jet wakes. The model employed here includes both acidic and organic aerosols-in their pure states and mixed with soot-as well as small ion clusters and electrically charged particles. The microphysical treatment accounts for the effects of charge, within the framework of a multicomponent size-resolved kinetically controlled vapor-aerosol system. Owing to their high proton affinities, water/acid solubility, and/or reactivities with liquid sulfuric acid and other inorganic compounds, certain organic constituents known to be generated by aircraft engines are likely to condense onto ions and charged particles and/or to be taken up by liquid sulfuric acid particles, where these particles are expected to act as efficient reaction sites. The present simulations, which are constrained by in situ measurements, indicate that in the case of very low sulfur emissions, organic species in the exhaust stream can dominate the mass of volatile particles detected at very early times. In the case of fuels with medium to high sulfur contents, the organic emissions may still contribute a significant fraction of the total aerosol mass and alter the composition of the exhaust particles. ¿ 1999 American Geophysical Union