Model calculations for the formation of aerosols and the interaction between themselves and with exhaust gases in plumes of cruising airliners are presented. A subset of in situ-nucleated H2SO4/H2O aerosols that stay liquid can transform into an almost pure HNO3/H2O mode because of enhanced uptake of HNO3. Soot embedded in a liquid coating containing H2SO4 and HNO3 triggers heterogeneous freezing of water ice and leads to visible contrails. At low temperatures and high fuel sulfur levels homogeneous freezing increases the ice mass. The ice particles may acquire a HNO3⋅3 H2O (NAT) coating upon evaporation of H2O, which can potentially lead to a lengthening of their lifetime. If future plume sampling experiments confirm these results, they would have important implications for ozone-related heterogeneous plume chemistry. ¿ American Geophysical Union 1996