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The impact of NOx emissions from aircraft upon the atmosphere at flight altitude 8-15 km


The objective of this project is to determine the emissions of NOX from aircraft engines and global air traffic at cruising altitudes, the resultant increase in NOX concentrations, and the effects on the composition of the atmosphere, in particular with respect to ozone formation in the upper troposphere.

A set of values for the effluent temperatures and concentrations at the exhaust of an engine has been established, in order to start the hot jet modelling. The work is then interactive between the different phases of the models. The first phase concentrates on the near field and the expansion of the hot jet. Preliminary results of the instantaneous values of the parameters along the first 25 meters are obtained with a simplified reaction scheme. The second phase looks at the mixing between the jet and the vortex. The adaptive grid algorithm has been developed and tested on a 2-dimensional test case for which it performs very well. Possible transformations along the wake, from short to long lifetime and from hot to cold temperatures are investigated. Preliminary measurements using gas chromatography corroborate the hypothesis that gas solid interaction may play an important role in the wake of an aircraft. A preliminary 3-dimensional database of nitrogen oxide emissions from aircraft has been provided. With this 3-dimensional input data transport simulations were performed with a spectral general circulation model with parameterizations of radiation, cloud formation and precipitation, convection, and vertical and horizontal diffusion. A similar numerical experiment was performed using a transport model including convection. The results of both models are qualitatively similar. The flight emissions also served as input for a 2-dimensional transport model with a simplified nitrogen oxide chemistry which was used to study the impact of aircraft emissions on the ozone concentration. First results have been obtained with respect to the dynamics of the jet flow and heterogeneous reactions on soot particles. Numerical simulations indicate large temperature fluctuations in the jet flow with possibly strong importance for the chemistry. Considerable progress has been made in developing global transport and circulation models including simple chemical cycles for both the tropo sphere and the stratosphere.

The AERONOX project investigated the emissions of nitrogen oxides (NOx) from aircraft engines and global air traffic at cruising altitudes, the resultant increase in NOx concentrations, and the effects on the composition of the atmosphere, in particular with respect to ozone formation in the upper troposphere and lower stratosphere. The project was structured into three subprojects: engine exhaust emissions; physics and chemistry in the aircraft wake; global atmospheric model simulations. A complementary programme of work by aviation experts has provided detailed information on air traffic data which was combined with data on aircraft performance and emissions to produce a global emissions inventory.

The work resulted in improved predictive equations to determine NOx emissions at cruise conditions based on available data for aircraft/engine combinations and NOx emission measurements on two engines in cruise conditions. This information was combined with traffic database to provide a new global NOx emissions inventory. It was found that only minor chemical cahnges occur during the vortex regime of the emission plume. However this result does not exclude the possibility of furthur changes in the dispersion phase. A variey of global models was set up to investigate the changes in NOx concentrations and photochemistry. Although aviation contributes only a small proportion (about 3%) of the total global NOx from all anthropogenic sources, the models show that aviation contributes a large fraction to the concentrations of NOx in the upper troposphere, in particular north of 30 degrees north.

For the analysis of the impact of aircraft emissions on the chemical composition of the troposphere, a 2-dimensional model was developed to describe photochemistry and transport processes in the upper troposphere at northern mid latitudes. The model included a simplified chemistry of nitrogen oxides and nitric acid and transport of trace species by advection, vertical eddy diffusion and convection. The nitrogen oxide sources considered were emissions at the Earth's surface, lightning, input from the stratosphere and aircraft emissions. The model when applied to the latitude band of 40 to 50 degrees north indicated an increase of nitrogen oxide in the upper troposphere on the order of 30 to 40% due to aircraft emissions. These calculations showed also the importance of fast vertical transport, for example, by deep convection for the budget of nitrogen oxides in the upper troposphere. To examine the change of concentration of ozone and hydroxyl radicals induced by aircraft emissions, reactions of hydroxyl radicals, hydrogen peroxy radicals (HO2), ozone, carbon monoxide and methane were included in the model. The calculations for the latitude band 40 to 50 degrees north showed a summertime increase of ozone and hydroxyl radical concentrations on the order of 3% and 10% repectively in the upper troposphere as a result of the increase of nitrogen oxides originating from aircraft.

For the study of the heterogenous conversion of nitrogen oxides to nitrogen acids on aerosol surfaces a large aerosol chamber was constructed with a double wall system: aluminium box (outside) and a Teflon-FEP bag (inside) Teflon-FEP is a perifluorinated copolymer of tetrafluorethene and hexafluoropropene. The chamber has a volume of 250 m{3} and a surface/volume ratio of 1 m{-1}. First experiments show half lives of about 21 days for the reactive gases ozone and nitrogen dioxide. The lifetime is limited by wall uptake and diffusion through the FEP walls. These long residence times enable slow reactions on aerosol surfaces to be studied.

The large aerosol chamber with a favorable surface to volume ratio of 1 m{-1} is operational, although clearly in a test phase. Contamination of the aerosol chamber is prevented by the double wall system and the permanent purging of the space between aluminium wall and the FEP bag. The long residence time of inert gases and the long half life of reactive gases are promising for future experiments. Experiments of typically 5 days duration will not be dominated by diffusion through the walls or wall reactions.
The project intends to set up a data base for the air traffic emissions. To achieve this, it is foreseen to combine engine emissions, measured and determined within this project, with an air traffic register, which will be established under the coordination of ECAC/ANCAT with DG XI. The influence of these emissions on the atmosphere will be determined by studying the physical & chemical processes within the aircraft wake and by calculating the 3D NOX concentration change with general circulation and chemistry models.

The project is divided into three major subprojects:

1. Engine Exhaust Emissions
2. Physics and Chemistry in the aircraft wake
3. Global atmospheric model simulations

Objective of Subproject 1 is to establish internationally acceptable reference data on aircraft engine emissions throughout the entire flight cycle up to 15 km. This is to be achieved by emission measurements on both engines and combustion rigs at altitude and ground level conditions in order to determine the correction factors, primarily for pressure, temperature, air mass flow and humidity effects. The emissions data will be combined with information on aircraft movements obtained from the air traffic register leading to a "Flight Emissions Data Base".

Objective of Subproject 2 is to study the fluid dynamics and the chemical kinetic processes in the wake and to find out the chemical composition of the wake after its size reaches the grid scale of the atmospheric models used in Subproject 3. It is intended to give a description of the gaseous and solid phase of the emissions in the jet and in the vortex regime and to study the mechanisms of interaction between the solid and gaseous phase and to determine the kinetic reaction constants involved in these mechanisms.

Aim of subproject 3 is to determine the three-dimensional NOX concentration change due to emission from aircraft, including both the climatological annual cycle of the concentration change and its long and short variability. Dispersion of airborne NOX will be simulated with two types of models: general circulation models and three-dimensional chemistry models.

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Linder Höhe
51147 KOELN

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Participants (14)