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Absorption measurements of SO2 isotopologues with application to sulfur isotope mass-independent fractionation during SO2 photolysis
PI: Stark, Glenn
We propose to measure high-resolution absorption cross sections for several isotopologues of SO 2 including 33 SO 2, 34 SO 2 , and 36 SO 2 from 180 to 220 nm. The measurements will be performed on a vacuum ultraviolet Fourier Transform Spectrometer at Imperial College, London. The data will be at sufficiently high resolution to resolve rotational structure, and will complement existing data for 32 SO 2. The measured cross section data will be interpreted by radiative transfer calculations in atmospheric photochemical models.
The expected results from this study are: i) measurement of high-resolution absorption cross section data for 33 SO 2 and 34 SO 2; ii) measurement of high-resolution cross section data for a mixture of ~ 50% 36 SO 2 and ~ 50% 32 SO 2; iii) incorporation of the cross section data for all isotopologues into a photochemical model of a low O 2 atmosphere. We will be able to constrain the magnitude of the mass-independent fractionation signature associated with SO 2 photodissociation, and possibly the concentration of sulfur in the Archean atmosphere. The cross section data will also be useful in existing photochemical models of the Archean atmosphere, and in constraining ab initio cross section calculations.
A key component of the “Early Evolution of Life and the Biosphere” research area is the geological and geochemical record in rocks. The discovery of sulfur mass-independent fractionation in ancient sedimentary minerals, and the strong likelihood that these signatures arise from atmospheric photochemical processes, implies that a complete understanding of the kinetics of atmospheric sulfur isotopes is essential to extracting the full implications of sulfur mass-independent fractionation to the composition and evolution of the early atmosphere. By measuring and interpreting high-resolution spectra for SO 2, a key component of the Archean sulfur cycle, we believe we can contribute significantly to understanding the full implications of sulfur mass-independent fractionation to the environment of the Archean and Paleoproterozoic Earth. The proposed study will contribute to our understanding of the O 2 and sulfur composition of the Archean and Paleoproterozoic Earth atmosphere.
