Chemiion concentration measurements in jet engine exhaust at the ground: Implications for ion chemistry and aerosol formation in the wake of a jet aircraft

Total positive chemiion concentrations n in jet engine exhaust at the ground were measured using an electrostatic probe. Data were obtained for two different engines (RR M45H and JT9D‐7) for one power setting (half thrust), two fuel sulfur contents (2 and 66 ppmm), and four distances d (1.39, 2.19, 4.19, and 18.6 m) behind the engines. The corresponding plume ages tp ranged from about 12 to 170 ms. As tp increases n decreases steeply from 1.6×108 cm−3 at tp = 12 ms to 3×106 cm−3 at tp = 170 ms. We conclude that this decrease mostly reflects ion removal by ion‐ion recombination with a mean rate coefficient of about 7.5×10−7 cm³/s. Our experimental findings have interesting implications for the chemical evolution and potential roles of chemiions in jet engine exhaust plumes. These implications are briefly addressed.