Study of stratosphere-troposphere exchange via 10Be/7Be isotope ratios

Full text: The present study is part of the European project STACCATO (influence of stratosphere-troposphere exchange in a changing climate on atmospheric transport and oxidation capacity). Stratosphere-troposphere exchange (STE) is one of the key factors controlling the budgets of ozone, water vapor and other substances in both the troposphere and the lower stratosphere. However, its contribution to their ozone budget relative to photo-chemical ozone formation from natural and anthropogenic precursor emissions is still uncertain. An international effort is made to estimate the strength of STE and its impact on tropospheric chemistry. The two cosmogenic radioisotopes of beryllium, 10Be and 7Be have very different half-lives of 1.51 Ma and 53.4 d, respectively. The combination of production rates, half-lives and different residence times in the stratosphere and troposphere, respectively, results in 10Be/7Be isotope ratios which can be used as fingerprints for STE. This ratio helps to give a much improved estimate of STE. However, only few 10Be measurements exist, because its detection requires the rather elaborate method of accelerator mass spectrometry (AMS). At the AMS facility VERA we are now measuring the 10Be content of air filters from the high-alpine stations 'Hoher Sonnblick', Austria, and 'Zugspitze', Germany. The TBe content is measured separately by decay counting. In this presentation, we want to describe the method of measuring 10Be with AMS, and to discuss the results of first 10Be/7Be ratios. (author)