Isotopic measurements of carbonyl sulfide

Sophie Baartman

This project involves the measurement of isotopologues of carbonyl sulfide (COS). It is part of the ERC project called COS-OCS (link to website). The aim of this sub-project is to perform the first, world-wide characterization of COS isotopes by measuring and modelling seasonal, latitudinal and altitudinal variations in the troposphere and stratosphere.

Carbonyl sulfide (COS) is the most abundant sulfur-containing trace gas in the atmosphere, with an average mixing ratio of 500 parts per trillion (ppt). It has a relatively long lifetime of about 2 years, which permits it to travel into the stratosphere. There, it likely plays an important role in the formation of stratospheric sulfur aerosols (SSA), which have a cooling effect on the Earth’s climate. Furthermore, during photosynthetic uptake by plants, COS follows essentially the same pathway as CO2, and therefore COS could be used to estimate gross primary production (GPP). Unfortunately, significant uncertainties still exist in the sources, sinks and global cycling of COS, which need to be overcome. Isotopic measurements of COS could be a promising tool for constraining the COS budget, as well as for investigating its role in the formation of stratospheric sulfur aerosols. We have built a pre-concentration and measurement system at IMAU that can measure COS isotopologues from samples, as well as semi-continuously from outside

Picture 1. The COS cycle and uncertainties

Picture 2. Sophie working on the COS system

The COS-OCS project was funded through the ERC-advanced funding scheme (AdG 2016 Project Number: 742798, Project Acronym: COS-OCS)