Massive positive and negative ions in the wake of a jet aircraft: Detection by a novel aircraft-based large ion mass spectrometer (LIOMAS)

Negative and positive chemiions (CI) were measured by an aircraft-based lar ge 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 distri butions were measured for mass numbers m up to 8500 atomic mass units, and additionally total fractional CI abundances f(M) for CI with m > 8500 were obtained. Very massive CI were observed even when nearly sulfur free jet fu el 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 sul fur, but more likely low volatility organic compounds (LVOC). However, when fuel with an FSC = 118 mg/kg was used a significant additional negative CT : growth was observed which must be due to sulfur-bearing molecules, probab ly sulfuric acid which is formed by oxidation of fuel sulfur. Use of the fu el with higher FSC did not change the size distribution of positive ions si gnificantly. For both FSC the negative ions had a larger mean m compared to the positive ions.