Summary Observations have shown that ozone levels in the upper troposphere (UT) and the lower stratosphere (LS) have changed over the last two to three decades. The observed reductions in the LS, which has been seen in the Northern Hernisphere during the last decade most probably are caused by man made emissions (CFCs and bromine compounds) in conjunction with particles and PSCs formation. For the UT, observations have shown an ozone increase for at least two decades, but less so the last few years. The causes of these changes are poorly understood. Modelling studies have been used to estirnate the impact of different man made sources on the chemical composition, and on ozone in particular in the UT and the LS.
These studies show that there are significant uncertainties in the estimates of the impact which are a result of limited knowledge of atmospheric processes and which have to be improved in order to come up with better estimates of the impact of aircraft emissions on ozone in the UT and the LS.
Emissions from aircraft (NOx, H20, SO2 and soot) at cruising altitudes are likely to affect the ozone chemistry in the UT and the LS in two ways: directly through enhanced photochemical activity (emission of NOx and water vapour), and through enhanced particle formation from NOx, water vapour and SO2. The impact of aircraft emissions is of particular importance to study, as the emissions are projected to grow rapidly over the next two decades compared to emissions from most other sources, and because there are significant regional differences in the impact on ozone and in the projected growth in the emissions. It is therefore likely that future aircraft emissions have the potential to perturb ozone levels significantly.
The overall objective of the study is to improve our scientific basis for estimates of the impact of aircraft emissions on the chemical composition in the UT and in the LS, and to perform 3-D model studies of the large scale (regional to hemispheric) perturbation of ozone from a projected future fleet of subsonic and supersonic aircraft. Focus in the study will be on two main areas: a) The role of heterogeneous processes in the UT and the LS and how these processes can be parameterised in global 3-D CTMs, and b) modelling studies of the future impact of subsonic as well as supersonic traffic on the ozone in the UT and the LS, with particular emphasis on the regional contribution to global scale ozone from regions with the largest projected traffic (Europe - US, South Asia and surrounding areas).
The tools for these studies will be state of the art 3-D CTMs (Chemical Tracer Models) available among the participating groups. The CTMs have different spatial resolution, transport parameterisation, and parameterisation of the chernical processes, including heterogeneous chemistry, and will therefore in a complementary way contribute to the overall objective of the project. The new AEROCHEM II project will build on the results obtained in the ongoing AEROCHEM project.
Ozone sonde data at northern latitudes collected during projects which has participated in European campaigns (e.g.
SESAME), and from aircraft measurements of ozone from the MOZAIC project are available through participation in the projects. These data will be used to compare with model distribution.
The project will provide important inputs to international assessments related to the Montreal Protocol (ozone) and to the IPCC process (climate). The process studies conducted in AEROCHEM and planned for AEROCHEM II will contribute to internahonal research programmes like the SPARC programme of the World Climate Research Programme (WCRP).
where the focus is on processes in the UT and the LS. It will also serve as a basis for decisions on selechons of the future generation of low emission engines for aircraft.
Funding SchemeCSC - Cost-sharing contracts
CB2 1EW Cambridge