Recent observations indicate rapid decline in ozone in the lowest regions of the stratosphere and models based on laboratory data and up-to-date representation of atmospheric transport show that this can be due to the ozone destroying reactions of BrOx and other stratospheric species. At the same time the concentrations of bromine containing source gases continues to increase. There is at present considerable uncertainty in the kinetics and photochemistry of several of the key processes involved in the atmospheric bromine chemistry. Such data are needed for an improved understanding of the role of bromine in the ozone balance for the lower stratosphere.
A programme of laboratory studies is proposed to provide quantitative kinetic and mechanistic data on selected gas phase, photochemical and heterogeneous reactions of bromine species. The gas phase work will cover key reactions which deplete ozone as well as those which control reservoir species. Several potentially important photochemical reactions involving bromine reservoir species will be studied.
Heterogeneous reactions will be studied both on bulk surfaces of sulphuric acid and water-ice and on aerosols of sulphuric acid particles. Surface uptake and reaction rates are more difficult to study than gas phase reactions, and novel experimental methods being developed by the participating groups will be used. Certain high-priority reactions, i.e. those to which ozone depletion is expected to be most sensitive, will be investigated by more than one technique to ensure the highest data quality.
The data for heterogeneous reactions will be brought together in a unifying physico chemical framework, which will then be used to formulate parameterisations of the reaction rates for atmospheric modelling. A preliminary assessment if the impact of the new data on atmospheric bromine and ozone depletion will be made using chemical transport models.
The work will be carried out by a consortium of leading European laboratories which have demonstrated expertise in the study of atmospheric reactions and have played a significant part in the development of the scientific knowledge related to the depletion of the ozone layer. The results will be communicated to the European stratospheric research community through the co-ordination provided in the EU programme.
Funding SchemeCSC - Cost-sharing contracts
OX1 3QZ Oxford