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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
Brief summary: 
How are reactive bromine and nitrogen cycled at the snow-atmosphere interface and what are their impacts on polar atmospheric oxidation capacity?
Importance of the area of research concerned: 
In polar regions, snowpack is a large reservoir of natural and synthetic chemical compounds. The exchange of chemically reactive gas-phase and particulate-phase compounds at the interface of the atmosphere-snow-ice system has been found to play an important role in the global environment and climate. In polar spring time, enhanced BrO concentration was measured over sea ice. BrO, as a strong oxidant, can cause severe ozone depletion and oxidise elemental mercury. However, the release of reactive bromine from snow is not fully understood and the emission flux is not well constrained and parameterized. Reactive nitrogen, an important precursor of ozone, can also be released from snowpack via photochemical reactions. Recent field data reveal evidence that the presence of reactive bromine can significantly accelerate nitrate formation, affecting the nitrogen budget. On the other hand, the presence of reactive nitrogen can also affect bromine cycling. Until now, the combination effect of snow-sourced reactive bromine and nitrogen on polar ozone have not been well explored, leaving a gap in our understanding of the dominant factors controlling polar atmospheric oxidising capacity.
Project summary : 
This project focuses on two important families of atmospheric chemical compounds – reactive bromine and nitrogen. In polar regions, they are both snow sourced, where they play a key role in influencing ozone production and loss. However, the relevant physical and chemical processes involved in the release of reactive bromine and nitrogen from snowpack and their joint effect on atmospheric ozone are not fully understood. Due to a lack of field data, their emission fluxes are not well constrained and parameterized, which prevents us from using numerical models to assess their environmental and climate impacts. In this project, we aim to fill this knowledge gap by deriving new emission schemes and using models to evaluate them. We will then use the updated model to assess snowpack emission on atmospheric self-cleansing capacity (ozone) and pollutant removal in a warming climate.
What will the student do?: 
The student will begin with compilating and reviewing the existing emission fluxes of reactive bromine and nitrogen from snowpack. The recent measurements of the physical and chemical parameters of the atmosphere and snow in the Arctic and Antarctica from various campaigns (eg MOSAiC) and stations (eg Eureka, Barrow and Halley) will be used to constrain and derive a new set of emission fluxes for reactive bromine and nitrogen. The derived new emission scheme will be implemented in UK Earth System Model (UKESM) for further evaluation. The updated model will be applied to quantify the individual and combined contribution of snow-sourced impurities (including from blowing-snow sourced sea salt aerosol) to polar and global atmospheric chemistry and environment. The student will then use the model to explore the feedback between changing sea ice (both extent and type of ice) and atmospheric oxidising capacity, from the recent past to present-day and into a warming climate (up to 2100). Overall, the project will build a new model version, with enhanced ability to reproduce near-surface NOx, BrO and ozone, for use on field campaign data and investigation of climate feedback cycles.
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.
Bond, A. M. H., Frey, M. M., Kaiser, J., Kleffmann, J., Jones, A. E. and Squires, F. A.: Snowpack nitrate photolysis drives the summertime atmospheric nitrous acid (HONO) budget in coastal Antarctica, Atmos. Chem. Phys., 23, 5533-5550,, 2023.
Yang, X., Strong, K., Criscitiello, A., Santos-Garcia, M., Bognar, K., Zhao, X., Fogal, P., Walker, K., Morris, S., and Effertz, P.: Surface snow bromide and nitrate at Eureka, Canada in early spring and implications for polar boundary layer chemistry, EGUsphere [preprint],, 2023.
You can find out about applying for this project on the British Antarctic Survey (BAS) page.