Cosmogenic 35S: A unique tracer to Antarctic atmospheric chemistry and the polar vortex
Résumé
The cosmogenic radionuclide 35S (half life ∼87 d) exists in both 35SO2 gas and 35SO42− aerosol phase in the atmosphere. Cosmogenic 35S fulfils a unique niche in that it has an ideal half‐life for use as a tracer of atmospheric processes, possesses a gas phase precursor and undergoes gas to particle conversion, providing a chronometer that complements other measurements of radiogenic isotopes of different half lives and chemical properties. Based on radiogenic 35S measurements and concomitant model calculations, we demonstrate that 35S is a unique tracer to understand stratospheric‐tropospheric air mass transport dynamics and the atmospheric oxidation capacity on a short time scale. Reported are the first measurements of 35S contained in SO42− aerosols (bulk and size aggregated) at Antarctica. 35SO42− concentrations at Dome C and Dumont D'Urville exhibit summer maxima and winter minima with a secondary winter peak. Higher oxidative capacity of the atmosphere and long range transport of mid latitude air increases 35SO42− activity in summer whereas a lack of air mass mixing coupled with low oxidant concentration in winter significantly decreases 35SO42− activity. A 3% contribution from stratospheric 35SO42− into the free troposphere during stratosphere‐troposphere air mass mixing accounts for the secondary winter 35SO42− peak. In the future, this work will be extended to 35S activity measurements of both gas and aerosol phases to further understand gas to particle conversion, vortex dynamics and trace polar stratospheric cloud sedimentation frequency.
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