Methyl chloride and methyl bromide are each the largest natural sources of chlorine and bromine in the stratosphere. Consequently, these compounds contribute to the destruction of the stratospheric ozone layer which protects flora and fauna from ultraviolet radiation that causes skin cancer and genetic damage. Sources and sinks of these compounds are not sufficiently well quantified with known sinks outweighing known sources by about 20% for both compounds. These unknown emissions, often referred to as “missing sources”, may complicate the prediction of the future state of the stratospheric ozone layer. It is currently assumed that stratospheric ozone levels are recovering due to the decrease of atmospheric concentrations of human-made chemicals, such as chlorofluorocarbons. Emissions from natural sources of methyl halides are, however, strongly dependent on temperature and thus on climate change. Higher temperatures, for instance, may cause increased emissions from oceans, plants and peatlands and counteract the decrease of atmospheric chlorofluorocarbon levels. Hence it is of great importance to better understand emission and degradation processes for these compounds in order to predict the future state of the ozone layer which protects us from the adverse effects of sunlight.
The overall objective of this project was to test and apply an isotopic approach for the characterisation of the main degradation pathway (sink) of these compounds in the atmosphere: the reaction with hydroxyl radicals. To achieve this goal, it was necessary to adapt and, if not available, to develop appropriate methods for the isotopic measurement of the various isotopes for these compounds. In a second step reference laboratory experiments were proposed to study hydroxyl radical reactions with methyl halides under controlled laboratory conditions and to determine the isotope effects caused by these reactions. These parameters are indispensable prerequisites for future studies that plan to use stable isotopes for source apportionment of methyl halides.
The applicant returned to the EU and was given the opportunity to reintegrate in a scientific environment in Germany where he amplified his research skills. Apart from maintaining previous collaborations, new contacts were established to deepen the scientific exchange. Additionally, the applicant benefitted from training in all aspects relevant for running international research projects such as managing the project, co-supervision of students and participating in teaching activities within and outside the host institution.
