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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
A polar wolf on the snowpack in the Arctic
Brief summary: 
How are reactive halogens and nitrogen cycled through polar snowpacks and what can they tell us about the oxidation capacity of the atmosphere?
Importance of the area of research concerned: 
The polar snowpack is a reservoir of natural and man-made chemical compounds, some of which are chemically reactive. Bromide and nitrate are two such compounds that play a critical role in polar atmospheric chemistry. Reactive bromine compounds (i.e. BrO and Br) are strong oxidants; they cause severe ozone depletion, oxidise elemental mercury, and also strongly influence the nitrogen cycle. However, it is far from clear and subject of an on-going debate: what the sources and source processes of reactive bromine are within the sea ice zone, where the largest bromine loading was observed on Earth. It has been suggested that both snowpack itself and windblown snow particles in the air can act as direct sources of bromine, however the existing parameterisations are not well constrained. For example, different models with different schemes implemented resulted in quite different conclusions regarding their individual role in polar bromine budget. This discrepancy has greatly affected the ability to use models to make any robust prediction for atmospheric oxidising capacity. Thus it is important to refine the parameters to allow a better representation of the snow emissions.
Project summary : 
This project builds on top of our previous work in this research field including both in-situ data collection, data analysis and numerical modelling. The existing parameterisations used in current chemistry models for reactive bromine and nitrogen emissions from snowpack and/or blowing snow need to be examined and well constrained before we can use them to make any reliable predictions in a changing climate. This project aims to (i) use newly collected and existing field data to evaluate and refine the parameterisations to allow a better representation of emission flux of reactive bromine and nitrogen from snowpack and blowing snow, and then (ii) apply the model to investigate changes in atmospheric self-cleansing capacity and pollutant removal above Arctic snow and sea ice taking into account ongoing rapid warming and profound changes of the cryosphere.
What will the student do?: 
The student will begin by examining the two existing major parameterisations regarding bromine emission from sea ice: the snowpack scheme and the blowing snow scheme. You are expected to implement the snowpack emission scheme to a global chemistry climate model (UM-UKCA), in which the blowing snow Br-emission scheme has already been implemented. In addition to that, you need to add a simplified snow NOx-emission scheme to the model based on our previous work. You will then use available field data to evaluate them. You will use the updated model to investigate 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). The project should produce a model with the ability to (i) output emission fluxes of reactive bromine and nitrogen under different snow/ice conditions (i.e. young ice vs multi-year ice, snow salinity, bromide and nitrate concentrations in snow), (ii) to reproduce near surface NOx, BrO in the air and bromide and nitrate in the snow at selected sampling locations to support field campaign data interpretation.
References - references should provide further reading about the project: 
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., 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., 2019.
Chan, H. G., Frey, M. M., and King, M. D.: Modelling the physical multiphase interactions of HNO3 between snow and air on the Antarctic Plateau (Dome C) and coast (Halley), Atmos. Chem. Phys., 18, 1507–1534,, 2018.
You can find out about applying for this project on the British Antarctic Survey (BAS) page.
Dr Rachael Rhodes
Dr Markus Frey
Dr Xin Yang
British Antarctic Survey Graduate Administrator