The formation and evolution of fine particles and ice contrails in an aircraft exhaust plume containing varying amounts of fuel sulfur have been simulated using an advanced aerosol microphysics model. The core sulfate and soot particles are tracked during the contrail formation and dissipation phases. When ion electrostatic effects are incorporated into the microphysics, sulfuric acid vapor emitted by high--sulfur--content fuels generates water--soluble particles that are large enough to be activated into contrails, improving the agreement between simulations and measurements. Our results also suggest that ice crystals formed in contrails efficiently scavenge vapors and particles, creating a sulfate aerosol accumulation mode that may contribute to cloud CCN/IN. The size distributions of aerosols produced both in the presence and absence of contrails agree reasonable well with the two characteristic types observed in the plumes of commercial aircraft. ¿ 1998 American Geophysical Union