Project highlights

  • Produce some of the first long-term global datasets of halogenated species derived from measurements by atmospheric nadir sounders
  • Monitor halogenated species in support of the Montreal Protocol
  • Investigate whether there is evidence for illegal emissions around the world, e.g. from East Asia.


Chlorofluorocarbons (CFCs) were first developed in the 1930s as safe, reliable, and non-toxic refrigerants for domestic use.  This explosion in use led to a steady increase in their atmospheric abundances.  However, while inert in the troposphere, it was this stability which enabled them to reach the stratosphere, where dissociation by ultraviolet (UV) radiation released chlorine atoms catalysing the destruction of the stratospheric ozone layer which protects us from harmful UV radiation.

It will be many years before stratospheric ozone levels return to pre-1980 levels because these species and their replacements, the majority of which are regulated by the Montreal Protocol, are generally very long-lived in the atmosphere.  Continued monitoring of these species is crucial to ensure abundances are decreasing as expected.  For example, atmospheric monitoring was able to quantify recent illegal emissions of CFC-11 from eastern China [Rigby et al., 2019].

Over recent decades, monitoring these species, which are also very strong greenhouse gases, from orbit has been the domain of infrared (IR) limb sounders.  The only active limb sounder now measuring these species regularly is the ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) which has been operating since 2004 [Bernath, 2017].  With the golden age of limb sounding coming to an end, one question is whether hyperspectral nadir IR sounders can fill the satellite monitoring gap.

A number of atmospheric nadir sounders, with low radiometric noise and high spectral resolution, measure top-of-atmosphere radiances in the thermal IR; these include IASI (Infrared Atmospheric Sounding Interferometer) and CrIS (Cross-track Infrared Sounder).  From the atmospheric spectra recorded by these instruments we can determine the concentrations of a range of trace gases, such as methane, water, and carbon dioxide.  These instruments have the potential to provide monitoring of halogenated species, and early work has shown the promise of using IASI for monitoring eight such species [De Longueville et al., 2021].  The advantage of using CrIS is that it possesses superior signal-to-noise, thus providing the prospect of more robust trends and the monitoring of additional species that IASI cannot observe.


University of Leicester


  • Climate and Environmental Sustainability


Project investigator

Dr Jeremy Harrison, National Centre for Earth Observation and University of Leicester ([email protected])


Prof John Remedios, National Centre for Earth Observation ([email protected])

How to apply


The student will primarily use data from IASI on MetOp-B (launched in 2012) and CrIS on Suomi-NPP (launched 2011).  A whitening transformation will be applied to averaged spectra, thereby removing most of the climatological background, and leaving a residual that contains the spectral signatures of trace gases that depart from normality [De Longueville et al., 2021]. These spectral aberrations can be attributed to changes in the abundance of trace species, and will be used to identify the detectable halogenated species such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and other related species such as SF6, CF4, and CCl4.  The student will then develop an algorithm to map the whitened signals of the identified halogenated species into robust total columns and trends, and compare these with ACE-FTS and ground observations, and the outputs of atmospheric models such as SLIMCAT.  The student will also investigate any evidence for illegal emissions on a regional scale.

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 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 ( 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

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.

If you wish to apply to the project, applications should include:

  • A CV with the names of at least two referees (preferably three and who can comment on your academic abilities)

Applications to be received by Wednesday 31st May 2023. 

Possible timeline

Year 1

Background review of atmospheric halogenated species, the IASI and CrIS instruments, and data analysis techniques.  An investigation into which halogenated species can be observed in the IASI and CrIS spectra.

Year 2

Development of an algorithm to map the whitened signals of the identified halogenated species into robust total columns and trends.

Year 3

Analysis of the data and comparison with ACE-FTS and ground measurements, and SLIMCAT calculations.  An investigation into whether the data reveal any illegal emissions on a regional scale.

Further reading

Bernath, P. The Atmospheric Chemistry Experiment (ACE). JQSRT, 186, 3-16 (2017).

Bernath, P., et al. Sixteen-year Trends in Atmospheric Trace Gases from Orbit. JQSRT, 253, 107178 (2020).

De Longueville, H., et al. Identification of short and long-lived atmospheric trace gases from IASI space observations. Geophysical Research Letters, 48, e2020GL091742 (2021).

Rigby, M., et al. Increase in CFC-11 emissions from eastern China based on atmospheric observations. Nature, 569, 546–550 (2019).

WMO (World Meteorological Organization), Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project–Report No. 58, 588 pp., Geneva, Switzerland, 2018.


It is not expected that this project will be affected by any future covid-19 restrictions.  The project is predominantly computer-based, and can be performed either in an office environment or remotely at home if necessary.  If working at home due to covid-19 restrictions, an internet connection is required in order to access university and NERC computing facilities, software and EO data.  Meetings with the supervisory team will be held safely and physically distanced, where permissible, or using online videoconferencing software.  The supervisory team are experienced at supervising projects remotely.