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Unlocking the fingerprint of air-snow-ice exchange of reactive bromine and nitrogen at the poles


   Polar Science for Planet Earth

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  Dr X Yang, Dr R Rhodes  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Brief summary: 

How are reactive bromine and nitrogen cycled at the atmosphere-snow-ice interface and what are their impacts on polar atmospheric oxidation capacity?

Importance of the area of research concerned: 

Snow on polar sea ice is a reservoir of natural and synthetic chemical compounds. Exchange of reactive gas- and particulate-phase compounds at the interface of the atmosphere-snow-ice system plays a key role in polar atmospheric chemistry. For instance, the highest loading of boundary layer BrO on Earth was observed above sea ice. Members of the family of reactive bromine species are strong oxidants, in particularly BrO and Br; they cause severe ozone depletion, oxidise elemental mercury, and also influence the nitrogen cycle by converting gaseous nitrogen oxides NOX (NO and NO2) to nitrate (NO3-). However, it is far from clear and subject of an on-going debate: what are the sources and production mechanisms of reactive bromine in the sea ice zone. It has been suggested that snowpack itself and windblown snow particles in the air can act as direct sources of reactive bromine. However, due to lack of field data, the emission fluxes are not precisely constrained so far, leaving a gap in quantifying polar bromine budget. This is a big problem because it prevents us from using numerical models to make robust predictions for changes in atmospheric oxidising capacity in warming climate.

Project summary : 

A warming climate will significantly change physical and chemical properties of sea ice and snow on ice, and then alter polar atmospheric environment, chemistry and climate. This project focuses on two important families of atmospheric chemical compounds – reactive bromine and nitrogen. Reactive bromine is predominantly emitted from saline interfaces as a result of either snowpack photochemistry or airborne saline particles generated by blowing snow. The aim of this project is to (i) constrain the emission flux for each of mechanisms using existing and newly collected data, (ii) use a numerical model to assess their relative contributions to atmospheric self-cleansing capacity and pollutant removal, and (iii) predict climate feedback taking into account the ongoing rapid warming and profound changes of the cryosphere. A state-of-the-art global chemical model (UKESM) will be our tool.

What will the student do?: 

The student will begin with compilating and reviewing existing emission fluxes for both reactive bromine and nitrogen, including the latest field data we collected from the Canadian High Arctic, as well as other data sets from field campaigns, such as snow physical and chemical properties and gaseous BrO and NOx concentrations in polar atmosphere. The next step of the project is to develop a new snow emission scheme and implement it to the UKESM-UKCA model. The new scheme will be evaluated against available datasets, including in-situ and remote sensing data, and the updated model will be applied in order to quantify individual source contribution to polar boundary layer bromine budget. The student will then use the model to explore the feedback of changing sea ice (both extent and type of ice) to atmospheric oxidising capacity from the recent past to the present, and into a warming climate (e.g. when the Arctic is ice free in the summer). Overall, the project will build a new model version, with enhanced ability to reproduce near-surface NOx, BrO reactivity, for interpretation of field campaign data and investigation of climate feedbacks.


Funding Notes

UK students will be eligible for a full NERC studentship. More information is available in the UKRI Training Grant Guide (https://www.ukri.org/apply-for-funding/before-you-apply/your-responsibilities-if-you-get-funding/meeting-ukri-terms-and-conditions-for-funding/)

A full studentship will include the cost of fees and a maintenance allowance. UKRI have confirmed that international students (EU and non-EU) will be eligible for all Research Council-funded postgraduate studentships from the start of 2021/2022 academic year. There will be a limited number of international studentships available

References

Yang, X., Blechschmidt, A.-M., Bognar, K., McClure–Begley, A., Morris, S., Petropavlovskikh, I., Richter, A., Skov, H., Strong, K., Tarasick, D., Uttal, T., Vestenius, M., and Zhao, X.: Pan-Arctic surface ozone: modelling vs measurements, Atmos. Chem. Phys. 20. Doi.org/10.5194/acp-20-15937-2020, 2020.
Yang, X., Frey, M. M., Rhodes, R. H., Norris, S. J., Brooks, I. M., Anderson, P. S., Nishimura, K., Jones, A. E., Wolff, E. W.: Sea salt aerosol production via sublimating wind-blown saline snow particles over sea ice: parameterizations and relevant microphysical mechanisms. Atmospheric Chemistry and Physics, 19. 8407-8424. 10.5194/acp-19-8407-2019, 2019.
Yang, X., Strong, K., Criscitiello, A. S., Santos-Garcia, M., Bognar, K., Zhao, X., Fogal, P., Walker, K. A., Morris, S. M., and Effertz, P.: Surface snow bromide and nitrate at Eureka, Canada in early spring and implications for polar boundary layer chemistry, submitted to Atmos. Chem. Phys. Discussion.
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