A numerical model including gas phase HOx, NOx, and SOx chemistry; H2SO4-soot adsorption; binary H2SO4-H2O nucleation; aerosol coagulation; and vapor condensation is used to investigate aerosol formation and growth in near-field aircraft plumes. The plume flow field is treated using the JANNAF standard plume flow field code, SPF-II. Model results are presented for a Mach 2.4 high-speed civil transport at 18 km altitude and 85 ¿N latitude and a subsonic Boeing 707 at 12.2 km, 47 ¿N. The results, based on hydroxyl radical driven oxidation kinetics, indicate that 1--2% of the emitted SO2 is converted to H2SO4 in the near-field exhaust (1--2 s) and that for typical exhaust SO2 emission indices (≈1 g kg-fuel) the plume is supersaturated with respect to both the pure liquid acid and H2SO4/H2O solutions. Classical nucleation theory predicts high levels of small (0.3--0.6 nm radius) H2SO4/H2O embryos. Coagulation and gas-to-particle conversion are followed to provide estimates for the number density of activated soot particles capable of serving as condensation nuclei for contrail formation. Results are presented illustrating the dependence of water condensation on the number density and size distribution of activated exhaust soot nuclei. ¿ American Geophysical Union 1996