The stratospheric sulfate aerosol layer is a key element in the climate system as it affects both the chemistry and radiative balance of the stratosphere. Carbonyl sulfide (COS) and sulfur dioxide (SO2) are the primary sources for stratospheric sulfate under volcanically quiescent conditions. SO2 is an important anthropogenic source of sulfur. The processes governing the transport of sulfur to the stratosphere are poorly quantified. Furthermore, the atmospheric lifetimes of these species are largely determined by hydroxyl (OH) concentrations and therefore changes in OH concentrations have a strong impact on the stratospheric sulfur burden. COS is the most abundant and long-lived sulfur containing source gas in the non-polluted atmosphere. Due to the paucity of atmospheric measurements of COS, our understanding of the dominant global sources and sinks of COS is incomplete. This incomplete knowledge has resulted in uncertainties in global COS budgets and the drivers of long-term trends in COS. To address these knowledge gaps the scientific goals of this research project include: (i) analysis of COS columns retrieved from the databases of Fourier Transform Infrared (FTIR) spectra measured at Lauder (New Zealand), Wollongong (Australia), and Arrival Heights (Antarctica) with the goal of establishing a climate data record of COS in the Southern Hemisphere (ii) investigating the transport of COS and SO2 from the base of the tropical tropopause layer (TTL) into the stratosphere using a Lagrangian (trajectory-based) chemistry transport model (ATLAS) and (iii) investigate the sensitivity of sulfur entering the stratosphere to tropospheric OH concentrations using ATLAS.