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

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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.