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Alia Khan dissertation defense

Thursday, July 14, 2016, 10:00AM - 12:00PM


Alia Khan


SEEC room N136 or Auditorium (TBD)


Quantifying sources, distribution, and processing of light absorbing aerosols in the cryosphere: A comparison of dissolved and refractory black carbon in polar and high mountain regions


Light absorbing aerosols (LAAs), such as black carbon (BC), in snow and ice are one of the least understood parameters in global climate models.  This is due to complicated physical processes within the cryosphere and too few in situ observations. BC is derived from the incomplete combustion of biomass and fossil fuels and can enhance melt water generation and glacial recession when deposited on snow and ice surfaces. Measurements are limited due to the difficulty of collecting and preserving samples for analysis from remote environments. In order to help build a larger repository of ground observations, BC concentration and composition in snow and glacial melt-water is explored across the polar regions in the Arctic and Antarctic, as well as major mountain regions such as the Himalayas, Rockies, and Andes Mountains. Three state-of-the-art methods are applied for BC detection.

The first chapter identifies chemical signatures of past and present sources of dissolved black carbon (DBC) in Antarctic lakes, using a DBC molecular marker method. Here we find that DBC with a woody signature is preserved in the deep, ancient brines of Antarctic lake bottom waters. In contrast, the surface waters are enriched in BC from fossil fuels. The second chapter, which also utilizes the DBC molecular marker technique, explores DBC concentration and composition across a global sample set from the cryosphere. Here we show the bottom waters of Antarctic lakes are surprisingly much more enriched in DBC compared to other regions of the cryosphere. The third and fourth chapters utilize the Single Particle Soot Photometer to measure refractory black carbon (rBC). The third chapter also applies spectral albedo measurements and the light absorption heating method to show that coal dust from an active mine in Svalbard, Norway significantly reduces the spectral reflectance of the surrounding Arctic surface snow. The fourth chapter reports aerosol rBC concentrations in the boundary layer of the McMurdo Dry Valleys, as well as in snow from the accumulation area of the Commonwealth Glacier. Here we determine that aerosol concentrations increase during katabatic wind events, but there is no significant trend in deposition in the snow pit. These findings support the importance of real in-situ observations in order to fully understand the role of BC in the global carbon cycle. Also, these ground-based measurements will likely serve as validation for future remote sensing of snow/ice impurities and LAAs deposition models.