The focus of this project is to use a number of numerical simulation to study the effects of the heterogeneous reactions on the composition of the middle atmosphere. More specifically the emphasis will be on the following topics:
- Implementation in existing two-dimensional models (2D) of microphysics codes which describe the evolution of aerosol particles.
- Detailed study of the influence of aerosol surface area on the two main heterogeneous reactions, that is hydrolysis of nitrogen pentoxide and chlorine nitrate, and consequently on the saturation of the NOx/NOy ratio.
- Application of the numerical code (microphysics and chemistry) to the analysis of a number of case studies as they results from specific campaign (EASOE, SPACE, AASE II, SESAME).
The upgrading of existing 2D models will result in a completely new class of numerical simulation tools. Two basic microphysics codes will be used for the implementation of a more realistic routine for the formation of stratospheric particles. The code prepared by the Danish Meteorological Institute will be used by the University of Oslo and the Belgian Institute for Aeronomy. The University of L'Aquila has developed its own code. These codes are able to simulate the growth of ice, sulfate and nitric acid trihydrate particles given the environmental condition on gas mixing ratios and temperatures.
A critical point in the implementation process is to make consistent the zonal averaged values intrinsic to the 2D models with the fact that especially in polar regions this may be an asymmetric process. The study of this complex situation will be one of the main justification for using also a general circulation model of the stratosphere and for developing three-dimensional mechanistic models. The general circulation model is coupled in a consistent way to the 2D model which includes photochemistry and tracer transport.
The upgrading of the models will open the possibility for testing other reaction mechanisms (like those including HNO4).
The effects of heterogeneous processes will be studied also in a number of observed situations where the analysis will be carried out with the help of assimilated data from the European Center (ECMWF) and NMC data. The use of these data coupled with a detailed microphysical code will help to understand the different properties of polar stratospheric cloud (PSC) particles between Northern and Southern Hemispheres in presence of rather different loading of background sulfate aerosols. This kind of study is particularly important because the surface area of PSCs available for heterogeneous chemical reactions in the stratosphere is closely related to a given meteorological condition and to the thermal history of a given air mass during its motion.
Funding SchemeCSC - Cost-sharing contracts