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Rapid Growth of Short-Lived Chlorocarbons in Earth’s Atmosphere: Implications for Ozone and Air Quality

   Lancaster Environment Centre

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  Dr R Hossaini, Dr O Wild  No more applications being accepted  Funded PhD Project (European/UK Students Only)

About the Project

Supervisors: Dr Ryan Hossaini (Lancaster), Dr Oliver Wild (Lancaster), Prof Lucy Carpenter (York), Prof Martyn Chipperfield (Leeds) and Dr Chris Wilson (Leeds)

Halogens (chlorine, bromine, iodine) play a key role in atmospheric chemistry and are implicated in a range of environmental issues. In the stratosphere (12-50 km), it is well established that anthropogenic halogen-containing gases (e.g. chlorofluorocarbons, CFCs), have caused widespread depletion of the ozone layer in recent decades. In consequence, production of CFCs and other long-lived ozone-depleting chemicals is now prohibited by the UN Montreal Protocol – a treaty to safeguard the ozone layer. Halogens also have a substantial influence on the chemistry of the troposphere, the lowest atmospheric region. Here, halogens alter the atmosphere’s oxidising capacity, and thereby affect the lifetime and global warming potential of greenhouse gases (e.g. methane), alter the production of aerosol, and promote adverse air quality at the surface.

So-called Very Short-Lived Species (VSLS) are a major source of airborne halogens. Some VSLS are naturally-emitted from the ocean (e.g. CHBr3, CH3I), while others are anthropogenic (e.g. C2Cl4, C2H4Cl2). Critically, unlike CFCs, these VSLS are not controlled by the Montreal Protocol and for some VSLS, their atmospheric abundance is increasing rapidly; surface levels of dichloromethane (CH2Cl2) have at least doubled in the northern hemisphere since 2000 (Fig. 1), with a growth rate of ~8 %/yr in the last decade. Sustained CH2Cl2 growth is attributed to an increase in industrial emissions. However, the precise sources of this and other VSLS are poorly characterised and it is unknown geographically where the increase in emissions is occurring.

This project combines state-of-the-art atmospheric modelling and analysis of observations to understand and quantify recent trends in CH2Cl2 and other VSLS. The student will (i) determine the key VSLS source regions, (ii) assess the atmospheric transformation of VSLS, and (iii) quantify their impact on atmospheric composition. A focus will be on understanding their impact on air quality over Asia, where elevated VSLS levels are found, and assessing how rising levels of VSLS could affect recovery of Earth’s ozone layer.

Further information:

Academic requirements: First-class or 2.1 (Hons) degree or Masters degree (or equivalent) in an appropriate subject.

Deadline for applications: The deadline for applications will remain open until the position is filled.

Start Date: October 2016

For further information or informal discussion about the position, please contact Dr Ryan Hossaini ([Email Address Removed])

Application process: Please contact Dr Ryan Hossaini ([Email Address Removed]) with an expression of interest and current CV in the first instance. Potential candidates will be interviewed and the deadline for applications will remain open until the position is filled.

You also require two references. Please download this reference form:

Send the form to your two referees and ask them to email it to Andy Harrod ([Email Address Removed]), Postgraduate Research Co-ordinator, Lancaster Environment Centre.

Funding Notes

Full studentship (UK/EU tuition fees and stipend (£14,057 [tax free]) for UK/EU students for 3.5 years. Unfortunately this studentship is not available to non-UK/EU applicants due to funding restrictions.


Hossaini, R., Chipperfield, M. P., Saiz-Lopez, A., Harrison, J. J., von Glasow, R., Sommariva, R., Atlas, E., Navarro, M., Montzka, S. A., Feng, W., Dhomse, S., Harth, C., Mühle, J., Lunder, C., O'Doherty, S., Young, D., Reimann, S., Vollmer, M. K., Krummel, P. B., and Bernath, P. F.: Growth in stratospheric chlorine from short-lived chemicals not controlled by the Montreal Protocol, Geophys. Res. Lett., doi:10.1002/2015GL063783, 2015.
Hossaini, R., Chipperfield, M. P., Montzka, S. A., Rap, A., Dhomse, S., and Feng, W.: Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone, Nature Geosci., 8, 186-190, doi:10.1038/ngeo2363, 2015.
Discussion of VSLS in Chapter 2 of the WMO/UNEP Scientific Assessment of Ozone Depletion 2014. Available here.
Leedham Elvidge, E. C., Oram, D. E., Laube, J. C., Baker, A. K., Montzka, S. A., Humphrey, S., O'Sullivan, D. A., and Brenninkmeijer, C. A. M.: Increasing concentrations of dichloromethane, CH2Cl2, inferred from CARIBIC air samples collected 1998–2012, Atmos. Chem. Phys., 15, 1939-1958, doi:10.5194/acp-15-19o39-2015, 2015.
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