The possible role of organics in the formation and evolution of ultrafine aircraft particles

We investigate the potential contribution of organic species emitted by air craft engines to the formation of ultrafine volatile particles detected in jet wakes. The model employed here includes both acidic and organic aerosol s-in their "pure" states and mixed with soot-as well as small ion clusters and electrically charged particles. The microphysical treatment accounts fo r the effects of charge, within the framework of a multicomponent size-reso lved kinetically controlled vapor-aerosol system. Owing to their high proto n affinities, water/acid solubility, and/or reactivities with liquid sulfur ic acid and other inorganic compounds, certain organic constituents known t o be generated by aircraft engines are likely to condense onto ions and cha rged particles and/or to be taken up by liquid sulfuric acid particles, whe re these particles are expected to act as efficient reaction sites. The pre sent simulations, which are constrained by in situ measurements, indicate t hat in the case of very low sulfur emissions, organic species in the exhaus t stream can dominate the mass of volatile particles detected at very early times. In the case of fuels with medium to high sulfur contents, the organ ic emissions may still contribute a significant fraction of the total aeros ol mass and alter the composition of the exhaust particles.