Identification of secondary aerosol precursors emitted by an aircraft turbofan

Abstract

Abstract. Oxidative processing of aircraft turbine-engine exhaust was studied using a potential aerosol mass (PAM) chamber at different engine loads corresponding to typical flight operations. Measurements were conducted at an engine test cell. Organic gases (OGs) and particle emissions pre/post PAM were measured. A suite of instruments, including a proton-transfer-reaction mass spectrometer (PTR-MS) for OGs, a multi-gas analyzer for CO, CO2, NOX, and an aerosol mass spectrometer (AMS) for non-refractory particulate matter (NR-PM1) were used. Total aerosol mass was dominated by secondary aerosol formation, which was approximately two orders of magnitude higher than the primary aerosol. The chemical composition of both gaseous and particle emissions were also monitored at different engine loads and were thrust dependent. At idling load (thrust 2.5–7 %), more than 90 % of the secondary particle mass was organic and could be explained by the oxidation of gaseous aromatic species/ OGs; e.g. benzene, toluene, xylenes, tri-, tetra-, and pentamethyl-benzene and naphthalene. The oxygenated-aromatics, e.g. phenol, furans, were also included in this aromatic fraction and their oxidation could alone explain up to 25 % of the secondary organic particle mass at idling loads. The organic fraction decreased with thrust level, while the inorganic fraction increased. At an approximated cruise load sulfates comprised 85 % of the total secondary particle mass.