Satellite Observation of Aviation Impacts on the UTLS

The well being of humanity relies on the environment in which we live, for example the atmosphere sustains the eco-system providing thermal insulation and protection from shortwave radiation. The region of the atmosphere from about 8-26 km comprising the upper troposphere and lower stratosphere (UTLS) plays a major role in the atmosphere's climate and on the surface environment, for example, changes in ozone in the lower startosphere have a large impact on the surface UV flux. Hence safeguarding the atmosphere from degradation is required for our continued existence.

Aerosols are particles ranging in size from 10^-3 to 30 micron and are produced by natural processes (e.g. volcanic dust, smoke from natural forest fires, condensation of atmopsheric gases) as well as by human activities. The primary anthropogenic aerosols include particles directly emitted during the combustion processes and indirectly formed from gases emitted during combustion.

In the 1970s, plans to build a large fleet of high-flying supersonic aircraft led to concerns that their exhaust emissions could cause a reduction in stratospheric ozone (Crutzen, 1971). In the end, only a small number of supersonic passenger aircraft were built, and attention switched to other possible causes of ozone depletion. However, in recent years, the growth in the number of long-haul subsonic passenger aircarft, and the projection for further expansion in the future, has reawakened a general concern for the effects of aircraft on the atmosphere. Specific concerns are the significance of emissions of H2O (an important greenhouse gas whose budget is poorly understood), NOx and aerosols on the radiative and chemical properties of the UTLS.

Present generation of aircraft passenger fleet spends a significant part of its time at cruise altitude within the lower stratosphere (WMO, 1992). As a result, the injection of chemically active compounds (NOx and H2O) and aerosol precursors (SO2 and Hydrocarbons) directly into the stratosphere could lead to ozone depletion (Brasseur, 1998). The forecast average growth rate of aricraft movement is about 5% per year (Schumann, 19994) so that even larger anthropogenic perturbations of the UTLS might be expected in the future.

Some of the most poorly understood processes associated with aircraft emissions are the heterogeneous reactions. The rate of these reactions is determined by the type and size distribution of aerosol particles which in turn are determined by the aerosols chemical and thermal history.

This study will focus on emissions at cruise altitude (i.e. in the lower atmosphere) as this is where aircraft spent significant part of their time and because the aircraft enhancement of the aerosol loading in the stratosphere will be typically 100 times greater than in the troposphere. The project will include the formulation of a detailed aerosol microphysical model in a chemical transport model of the stratopshere. The resulting model will be used to simulate the evolution of startospheric aerosol properties including aircraft emission.

Scientific objectives of the project