This multidisciplinary project is aimed at investigating the physical and chemical processes involving particles of polar stratospheric clouds (and other stratospheric aerosols), and the potential role of these processes in the chemistry of the stratosphere.
The project will include the measurement of significant laboratory data for the development of models of aerosol catalysed reactions relevant to the depletion of ozone. The results will be confronted to the result of field measurements.
The main elements of the project are as follows:
In-situ measurements of stratospheric aerosols, trace gases and cluster ions with high resolution altitude measurements. Such vertically resolved profiles of concentration will allow the study of the formation and destruction of PSC particles as well as their roles in processing trace gases.
The second part consists of an extensive experimental programme concerning the thermodynamics and physico-chemistry of ice and hydrate particle. The aims are to understand and to quantify the different elementary steps leading to the conversion of passive to active chlorine molecules on stratospheric aerosols using laboratory simulation. The steps to be studied are the following: condensation and evaporation of ice and hydrate particles, sticking and adsorption of trace gases on particle surfaces, diffusion of hydrogen chloride into ice, heterogeneous reactions of ClONO2 and nitrogen pentoxide with water and HCl on ice or hydrate particles, and release of HOCl , chlorine and/or ClONO.
The third part is computer modelling of ice-catalysed reactions using classical trajectory calculations simulating chemical processes and reactions occurring on ice crystals. This approach is complementary to the experimental one to allow detailed understanding of the contribution of each elementary step in the overall process.
In order to evaluate the role of heterogeneous processes on ozone chemistry, vertical profiles of various key chemical species (simulated by model calculations using heterogeneous chemistry kinetic data) will be compared with in-situ measurements.
Funding SchemeCSC - Cost-sharing contracts
CB2 1TN Cambridge