Investigations of the Global Budget of Carbonyl Sulfide Using Data Assimilation of Surface and Satellite Observations

Abstract

Carbonyl sulfide (COS) is a significant trace gas in the atmosphere. It is taken up by ecosystems and proves useful in tracking gross primary production (GPP). However, our understanding of COS is insufficient, given that it originates from various sources and undergoes various pathways in the atmosphere. In this thesis, I employ inverse modeling and data assimilation techniques to address several critical questions and advance our understanding of the global budget and cycle of COS. The sources and sinks of COS are not balanced, suggesting the existence of missing sources in the global COS budget. Utilizing the inverse model TM5-4DVAR, I assimilate data from the NOAA surface network, pinpointing these missing sources in tropical oceans and underestimating sinks in northern high latitudes. Additionally, I collaborate with international scientists to execute a TransCom-COS protocol, where we transport state-of-the-art fluxes from the TM5-4DVAR and LMDz inversions into seven atmospheric transport models. The results exhibit good agreement between the inversions and alignment with model simulations based on aircraft observations. Furthermore, I assimilated MIPAS satellite observations to enhance the initial inverse model. The MIPAS satellite data significantly improves the inversions, particularly in distinguishing between fluxes from oceans and land. Sulfur isotopes within COS are also a captivating topic of study. Therefore, I utilize TM5 to simulate the isotopic composition and explore the influence of photolysis and vertical resolution on COS isotope signatures in the stratosphere. The investigations within this thesis will contribute to our comprehension and broaden our knowledge of the global cycle and budget of COS.