2024-L18 Carbonyl sulfide (COS) as climate diagnostic: re-evaluating the infrared spectroscopy used for remote sensing of the Earth’s atmosphere

Project highlights

A complete laboratory re-evaluation of the infrared spectroscopy of carbonyl sulfide (COS)
Production of a new COS linelist to improve remote-sensing observations of COS
The opportunity to work with retrieval scientists and investigate COS as a climate diagnostic

Overview

Planet Earth has a number of natural climate-regulating mechanisms, including the biospheric uptake of carbon by vegetation and the abundance of stratospheric sulfate aerosols (SSA). The former directly removes some carbon dioxide (CO2) emissions from the atmosphere, while the latter have a cooling effect on climate. Both mechanisms are intrinsically linked to the trace gas carbonyl sulfide (COS or OCS).

COS is the most abundant sulfur-containing molecule in the atmosphere. The dominant source is biogenic activity in the oceans, while the sinks are due to uptake by vegetation (by the same initial pathway as CO2) and destruction in the stratosphere (SSA formation). Despite this importance, its atmospheric sources and sinks are not well quantified. There is a growing recognition that COS can be used as a climate diagnostic, and that a better understanding of its atmospheric variations will lead to a deeper understanding of CO2 uptake and SSA formation, and the responses of these to our changing climate. Remote-sensing observations have a crucial role to play in this respect since they provide a global view of COS that is not otherwise possible.

Observations of COS are made from a number of satellite instruments using different infrared bands: the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS; limb) which utilises the strongest ν3 band at 2062 cm-1, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS; limb) instrument which utilises the weaker ν1 band at 858 cm-1, and the Infrared Atmospheric Sounding Interferometer (IASI; nadir) instruments which utilise the ν3 band. Additionally, ground measurements as part of the Network for the Detection of Atmospheric Composition Change (NDACC) utilise the ν3 band, as does the balloon-borne JPL MkIV interferometer which also uses the weaker ν1+ν3 and 2ν3 bands for the lowest altitudes.

HITRAN contains a COS linelist that has been utilised for all these remote-sensing observations. In order to improve these observations, we require reference COS spectroscopy that is accurate and robust. However, the HITRAN linelist has a number of deficiencies that urgently need to be resolved. Uncertainties in the line intensities can vary from 5% to 20%; this needs to be reduced to under 1%. This work will be the first detailed laboratory study of COS lineshape parameters and their temperature dependences. They will directly improve the observational data products.

Host

University of Leicester

Theme

Climate and Environmental Sustainability

Supervisors

Project investigator

Dr Jeremy Harrison (University of Leicester, email: [email protected])

Co-investigators

Prof John Remedios (NCEO)

How to apply

Each host has a slightly different application process.
Find out how to apply for this studentship.
All applications must include the CENTA application form.
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Methodology

In this project, the student will perform a complete re-evaluation of the IR spectroscopy of COS. This will involve utilising a state-of-the-art Bruker IFS 125HR Fourier transform spectrometer at the new National Centre for Earth Observation (NCEO) SPectroscopy for ENvironmental SEnsing Research (SPENSER) laboratory at Space Park Leicester. Infrared spectra will be recorded for both pure and air-broadened COS over a range of temperatures and pressures. These will be analysed to produce a robust COS linelist that will provide a more accurate basis for COS retrievals from remote-sensing observations.

We will collaborate with the ACE-FTS and MIPAS (IMK-KIT) retrieval teams to investigate how the new linelist improves the retrievals and resolves observed biases. We will also implement the new spectroscopy within the NCEO-Leicester IASI COS retrieval scheme, building on the work of a previous PhD student. These IASI satellite observations are a key part of the NCEO’s national capability International Science programme which runs until March 2026. The student will have the opportunity for their work to feed into this programme, in particular into global COS inversions in collaboration with NCEO-Leeds.

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

This studentship provides an exciting opportunity to work with cutting-edge spectroscopy measurements, satellite observations and atmospheric radiative transfer techniques in a challenging area of atmospheric science. This project covers a range of topics: atmospheric spectroscopy; remote sensing; retrieval techniques; atmospheric chemistry; data visualisation & analysis. The National Centre for Earth Observation (NCEO) will provide additional training opportunities via its Researchers’ Forum and regular conferences/workshops, and enable the student to interact with scientists working in Earth Observation on a national level. There will also be the opportunity to attend and present at international conferences.

Partners and collaboration

The student will be based at the new Space Park Leicester facility and work within the National Centre for Earth Observation (NCEO). The NCEO (www.nceo.ac.uk) is a distributed NERC centre providing the UK with national capability in EO science. The student will therefore be exposed to a wide range of research techniques in a multi-disciplinary research environment.

Further details

Further details on how to contact the supervisor for this project and how to apply for this project can be found here:

Interested applicants are invited to contact Dr Jeremy Harrison ([email protected]). Note that all potential applicants are strongly advised to make contact before applying.

To apply to this project:

You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2024.
You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities.
Please submit your application and complete the host institution application process via: https://le.ac.uk/study/research-degrees/funded-opportunities/centa-phd-studentships. Please scroll to the bottom of the page and click on the “Apply for NERC CENTA Studentship” button. Your CV can uploaded to the Experience section of the online form, the CENTA application form 2024 can be uploaded to the Personal Statement section of the online form. Please quote CENTA 2024-L18-CENTA2-PHYS2-HARR  when completing the application form.

Applications must be submitted by 23:59 GMT on Wednesday 10th January 2024.

Dr Jeremy Harrison is the NCEO’s spectroscopy leader and capability leader in atmospheric radiative transfer. Based in the Earth Observation Science (EOS) group at the University of Leicester, his expertise lies in atmospheric spectroscopy, atmospheric radiative transfer, and the remote sensing of trace gases.

Possible timeline

Year 1

Literature review; learn how to operate the state-of-the-art Bruker IFS 125HR Fourier transform spectrometer at Space Park Leicester; begin laboratory measurements of OCS over a range of pressures and temperatures.

Year 2

Finish laboratory measurements; learn and apply the multispectrum fitting technique to the recorded spectra.

Year 3

Produce a final COS linelist; interact with retrieval scientists (IASI, MIPAS, ACE) to produce new retrieved mixing ratios; determine how the new spectroscopic data improves the retrieved data.