Massive positive and negative chemiions in the exhaust of an aircraft jet engine at ground-level: mass distribution measurements and implications for aerosol formation

Mass distributions of positive and negative chemiions (CI) were measured in the exhaust plume of an aircraft jet engine at the ground at exhaust gas ages around 0.1 s using an ion mass spectrometer with a mass range of 8500 amu (large ion mass spectrometer, LIOMAS). Most of the CI had mass numbers m<2000, but very massive CI with m up to at least 8500 were also observed. About 1% of the negative CI and 0.2% of the positive CI had m>8500. An increase of the fuel sulfur content from 2 to 66 mg/kg did not change the ion mass distributions. This indicates that most of the observed CI did not contain sulfur-bearing molecules, but probably contained low volatility organic compounds (LVOC). An LVOC-emission index of 22.5 mg LVOC/kg fuel is inferred from our data.