Isotopic fingerprints of carbonyl sulfide (COS) in atmosphere and biosphere

羰基硫（COS）是CO2的硫类似物。它是最丰富的大气硫化合物，寿命为2至4年。COS有工业和自然来源，主要是海洋。其主要汇是植物和土壤吸收，但由于其寿命长，一些COS到达平流层，在那里它经历光解和氧化为硫酸盐，形成平流层气溶胶层（图1）。这一层对臭氧化学、辐射平衡和地球气候至关重要。与CO2一样，COS在光合作用过程中被吸收，但在呼吸过程中不被释放，使其成为总初级生产力的示踪剂（Asaf等人，2013年）。然而，植物和土壤吸收的重叠限制了COS浓度单独用于此目的。同位素测量最近已在确定COS源和汇（包括大气氧化途径）的指纹方面得到应用，一种新的COS同位素在线分析方法将用于13 C和34 S的测量（Hattori等人，2015），并进一步扩展到多同位素体（13 C16 O34 S）的同位素分馏。土壤和植被吸收COS过程中的同位素分馏将使用COS-浓缩大气，以便对不同的COS汇的相对贡献提供限制。将测量COS在真实光照条件下光解过程中的同位素分馏，并将其用于验证平流层硫酸盐气溶胶收支。最后，将在存档的对流层和平流层样品上采用新方法，以改进COS的全球收支，从而量化总光合作用速率。化学、物理或地球科学学位是可取的。将提供同位素质谱、气体和真空系统、仪器控制和数字数据分析方面的培训。任何科学知识空白都可以通过参加讲授课程来填补，例如地球化学循环和大气化学。该项目包括访问在荷兰的国际合作者。

BackgroundCarbonyl 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.MethodologyA 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 trainingThis 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.