Abstract
The impact of aircraft exhaust particles on human health and climate are raising concerns globally. Particle number concentrations in exhaust plumes of turbofan jet engines, which are commonly used in civil aviation, are generally dominated by volatile particles (sulfates or organics) rather than nonvolatile particles (mostly soot). However, the mechanism of emission and formation of volatile particles are unclear. Here, we evaluated the exhaust particles from turbofan engines at the engine exit and downstream. In downstream samples, the number of soot particles with scattering-layered graphene-like structures, typically generated by combustion, was <1% of the total number of particles analyzed. The remaining fraction predominantly contained trace amorphous, amorphous, and onion-like particles that partially contain graphene-like circular layers. The microphysical structures of these three types of particles in aircraft exhaust plumes were newly identified. They were mainly single spherical particles with diameters of ∼10-20 nm, suggesting that they were formed via nucleation and partial pyrolysis and were not significantly affected by coagulation with preexisting soot particles. The unique internal structures of these particles may affect their physicochemical properties, including volatility, surface reactivity, and solubility, and potentially impact their interaction with the human respiratory tract.