Negative and positive chemiions (CI) were measured by an aircraft-based large ion mass spectrometer (LIOMAS) in the wake of a jet aircraft (ATTAS) at an altitude of 8 km and at plume ages between 0.6 and 6.2 s. CI mass distributions were measured for mass numbers m up to 8500 atomic mass units, and additionally total fractional CI abundances fM for CI with m>8500 were obtained. Very massive CI were observed even when nearly sulfur free jet fuel was burnt in the ATTAS engines (fuel sulfur content FSC=2 mg/kg). This indicates that a CI growth process was operative which did not involve sulfur, but more likely low volatility organic compounds (LVOC). However, when fuel with an FSC=118 mg/kg was used a significant additional negative CI growth was observed which must be due to sulfur-bearing molecules, probably sulfuric acid which is formed by oxidation of fuel sulfur. Use of the fuel with higher FSC did not change the size distribution of positive ions significantly. For both FSC the negative ions had a larger mean m compared to the positive ions. ¿ 2000 American Geophysical Union