Transport of Bromine into the Atmosphere in Polar Regions

Ph.D. Dissertation, 2016, Engineering, Thayer School of Engineering, Dartmouth College

Abstract: Polar tropospheric ozone depletion events (ODE) are an early springtime phenomena strongly correlated with increased concentrations of reactive bromine gases (BrO and Br), whereby Br serves as a catalysis in the breakdown of ozone into oxygen through a series of photochemical and heterogeneous reactions. This process involves the autocatalytic production of reactive bromine from bromide ions originating in the ocean, in what is termed the "bromine explosion." During an ODE, atmospheric oxidation potentials can be altered, with unique halogen oxidation pathways dominating atmospheric chemistry, resulting in consequences such as the depletion of gaseous mercury and subsequent mercury deposition in polar regions. However, the mechanism by which Br enters the troposphere is not well understood. Sea ice is known to play a critical role in mediating the exchange of heat, gases, and chemical species across the ocean-atmosphere interface. This research focuses on the transport of Br, which originates in sea water and is hypothesized to enter the atmosphere via blowing snow over first year sea ice. Using ion chromatography, x-ray micro-computed tomography, synchrotron x-ray micro-fluorescence, and scanning electron microscopy, we aim to identify the microstructural and stratigraphic location of Br and other salts in the snow and ice. Knowing whether these salts exist at grain boundaries or deeper within the crystal lattice helps assess the potential that blowing snow can loft Br into the atmosphere. With the ratio of first-year to multi-year sea ice increasing with climate change, understanding this mechanism is critical for assessing the impact of ODEs on future atmospheric chemistry.

- Bromide: It's What's Blowing in the Wind. Ice and Climate Seminar, Dartmouth College, NH. April 22, 2014.
- Salty Snow and Radical Reactions: The Activation of Bromide in the Sea Ice Zone. Department of Mathematics, University of Vermont, Burlington, VT. April 26, 2013.
- Bromide in Snow in the Sea Ice Zone. McMurdo Station Sunday Talks, Ross Island, Antarctica. October 28, 2012.
- Salty Snow and Radical Reactions: The Activation of Bromide in the Sea Ice Zone. University of Otago, Dunedin, New Zealand. September 27, 2012.
- Salty Snow and Radical Reactions. Ice and Climate Seminar, Dartmouth College, NH. August 7, 2012.
- Life in the Cold. Cohasset High School, Cohasset, MA. May 4, 2012.

- Lieb-Lappen, R. M.; Obbard, R. W. 2015. The Role of Blowing Snow in the Activation of Bromine over First-Year Antarctic Sea Ice. Atmos. Chem. Phys. 15: 7537-7545. doi:10.5194/acp-15-7537-2015.
- Obbard, R. W., Lieb-Lappen, R. M., Nordick, K. V., Golden, E. J., Leonard, J. R., Lanzirotti, A., Newville, M. G. 2016. Synchrotron X-Ray Fluorescence Spectroscopy of Salts in Natural Sea Ice. Earth Space Sci. 3. doi: 10.1002/2016EA000172.
- Ph.D. Dissertation: How Sea Ice Microstructure Influences the Polar Transport of Salts from the Ocean into the Atmosphere.

Advisor: Rachel Obbard