Dr Alina Marca (UEA)
Prof Thomas Röckmann (Utrecht University)
Carbonyl sulfide (COS) is a sulfur-analogue of CO2. It is the most abundant atmospheric sulfur compound and has a lifetime of 2 to 4 years. COS has industrial and natural sources, mostly the oceans. Its main sinks are plant and soil uptake, but due to its long lifetime, some COS reaches the stratosphere where it undergoes photolysis and oxidation to sulfate and forms the stratospheric aerosol layer (Fig. 1).
This layer is of key importance for ozone chemistry, the radiation balance and Earth’s climate. Just as CO2, COS is taken up during photosynthesis, but not released during respiration, making it a tracer for gross primary productivity (Asaf et al. 2013). However, overlap of plant and soil uptake limit the use of COS concentration alone for this purpose. Isotope measurements have recently found applications in fingerprinting COS sources and sinks including atmospheric oxidation pathways, and can potentially distinguish between plant and soil uptake.
A novel online method for isotope analysis of COS will be used for 13C and 34S measurements (Hattori et al. 2015) and further extended to polyisotopologues (13C16O34S) on mass-spectrometers with worldwide unique analyser and detector configurations.
The isotope fractionation during COS uptake by soils and vegetation will be determined using COS-enriched atmospheres, in order to provide constraints on the relative contributions of different COS sinks. Isotope fractionation during COS photolysis under realistic light conditions will be measured and used to verify the stratospheric sulfate aerosol budget.
Finally, the new method will be deployed on archived tropospheric and stratospheric samples to improve the global budget of COS for the quantification of gross photosynthesis rates.
Person specification and training
This project requires good quantitative-analytical and experimental skills. A degree in chemistry, physics or earth sciences is desirable. Training will be provided in isotope mass spectrometry, gas and vacuum systems, instrument control and numerical data analysis. Any scientific knowledge gaps can be filled by attending taught courses, e.g. in biogeochemical cycles and atmospheric chemistry. The project includes visits to international collaborators in the Netherlands.