Improving Retrievals of Atmospheric Carbonyl Sulphide (OCS) from Ground-based Remote Sensing Spectrometers

Abstract:

Changes in the carbon cycle both drive and respond to climate change, but many of the underlying processes are not well understood. The carbon cycle is a complex system, and atmospheric measurements of CO₂ alone are often insufficient to distinguish between the processes at work in the terrestrial carbon cycle, specifically photosynthesis and ecosystem respiration. Recent studies have shown potential for an atmospheric trace gas, carbonyl sulphide (OCS), to be used as a proxy for photosynthesis.

Our work focuses on improving retrievals of OCS from solar absorption spectra recorded by ground-based Fourier transform spectrometers. Our goal is to use these measurements to help enhance our understanding of the processes driving changes in the terrestrial carbon cycle. We focus our analysis on spectra recorded by spectrometers that are part of the Total Carbon Column Observing Network (TCCON). The TCCON uses a profile scaling retrieval algorithm to calculate column-averaged dry-air mole fractions (X_G, for gas G) for many atmospheric gases. The TCCON retrieval is therefore sensitive to the shape of its a priori vertical profile. We will present results comparing our new X_OCS retrievals and the in situ OCS concentration measurements from the NOAA Carbon Cycle Aircraft Network. These comparisons are used to improve the shape of the OCS prior profiles, which improve the X_OCS retrievals, and to place the X_OCS measurements onto the NOAA trace gas standard scale.