SMALL-SCALE CHEMICAL EVOLUTION OF AIRCRAFT EXHAUST SPECIES AT CRUISING ALTITUDES

The chemical transformation of exhaust trace species in aircraft plume s, both directly emitted by the airplane and generated in situ within the first few kilometers behind a single jet engine, is investigated. The chemical processes are strongly coupled to the turbulent dynamics of the hot jet which rapidly mixes with the surrounding atmospheric ai r. Key issues of the chemical reactions in the jet regime are worked o ut and the results of extensive parameter studies are presented. The e volution of hydrogen, oxygen, nitrogen, and sulfur species is discusse d in detail and related to observations. Spatially resolved, two-dimen sional simulations are compared with box model calculations to point o ut specific features that result from the coupling between mixing and chemistry and to answer the question under which conditions box models can be applied to give a reasonable description of the jet plume chem istry. Main results concern the conversion efficiencies of primary int o secondary exhaust products, the oxidation potential within young air craft plumes to produce nitrous, nitric, and sulfuric acid, the sensit ivity of these processes under variation of exit plane conditions, as well as the production of new aerosol particles. Open questions concer ning chemical processing in near-field exhaust plumes are addressed. T he modeling framework presented in this study serves as a basis for fu rther near-held studies on the physics and chemistry in aircraft wakes .