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).
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.
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, however this has some 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 improve the spectroscopy of COS by providing the first detailed laboratory study of COS lineshape parameters and their temperature dependences. Also in need of improvement is the ν1+ν2 band of CO2 at 2077 cm-1, which overlaps with the COS ν3 band.
This project is a CENTA Flagship Project.
This project is suitable for CASE funding
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The candidate will perform a re-evaluation of the infrared spectroscopy of COS. This will involve new measurements at the NCEO SPectroscopy for ENvironmental SEnsing Research (SPENSER) laboratory at Space Park Leicester. There will also be the opportunity to visit the PTB in Braunschweig, Germany, which has additional laboratory facilities for the characterisation of gas samples to metrological accuracy. Infrared spectra will be recorded for both pure and air-broadened COS over a range of temperatures and pressures, and these will be analysed to produce a more accurate COS linelist. The candidate will also measure and analyse the ν1+ν2 band of CO2, which is an important interferer for the COS ν3 band. The candidate will investigate how the new spectroscopy improves ACE-FTS, MIPAS, and IASI retrievals, with a particular emphasis on validating these data for the NCEO-Leicester IASI COS retrieval scheme.
DRs will be awarded CENTA Training Credits (CTCs) for participation in CENTA-provided and ‘free choice’ external training. One CTC can be earned per 3 hours training, and DRs must accrue 100 CTCs across the three and a half 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.
The candidate will be based at Space Park Leicester 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 candidate will be exposed to a wide range of research techniques in a multi-disciplinary research environment.
This project has been developed in collaboration with the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. The successful applicant will have the opportunity to visit the PTB to perform spectroscopic measurements. The PTB has additional laboratory facilities for the characterisation of gas samples to metrological accuracy.
Year 1: Literature review; learn how to operate a Bruker IFS 125HR Fourier transform spectrometer; begin laboratory measurements of OCS over a range of pressures and temperatures.
Year 2: Finish laboratory measurements of OCS; perform measurements of CO2; learn and apply the multispectrum fitting technique to the recorded spectra.
Year 3: Produce final linelists; investigate implications of new data on atmospheric radiative transfer; validate the new spectroscopy against atmospheric satellite observations (IASI, MIPAS, ACE).
Cartwright et al.: Global Optimal Estimation Retrievals of Atmospheric Carbonyl Sulfide Over Water from IASI Measurement Spectra for 2018, Atmos. Chem. Phys., https://doi.org/10.5194/egusphere-2025-1073, in press.
Glatthor et al.: Global carbonyl sulfide (OCS) measured by MIPAS/Envisat during 2002–2012, Atmos. Chem. Phys., 17, 2631–2652, https://doi.org/10.5194/acp-17-2631-2017, 2017.
Ma et al.: Inverse modelling of carbonyl sulfide: implementation, evaluation and implications for the global budget, Atmos. Chem. Phys., 21, 3507–3529, https://doi.org/10.5194/acp-21-3507-2021, 2021.
Sung et al.: Line strength measurements of carbonyl sulfide (16O12C32S) in the 2v3, v1+2v2+v3, and 4v2+v3 bands, JQSRT, 110, 2082-2101, https://doi.org/10.1016/j.jqsrt.2009.05.013, 2009.
Whelan et al.: Reviews and syntheses: Carbonyl sulfide as a multi-scale tracer for carbon and water cycles, Biogeosciences, 15, 3625–3657, https://doi.org/10.5194/bg-15-3625-2018, 2018.
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.
Interested applicants are invited to contact Dr Jeremy Harrison ([email protected]). Note that all potential applicants are strongly advised to make contact before applying.
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