| Summary: | Ice nucleating particles (INPs) in the Arctic can influence climate and precipitation in the region; yet our understanding of the concentrations and sources of INPs in this region remain uncertain. The following dissertation investigates 1) the properties and concentrations of INPs in the sea surface microlayer and bulk seawater samples collected in the Canadian Arctic, and 2) the source region of measured concentrations of INPs in the Canadian Arctic marine boundary layer. All measurements were made in the Canadian Arctic on board the CCGS Amundsen during the summers of 2014 and 2016. INPs were ubiquitous in the microlayer and bulk seawater samples, and were likely heat-labile biological materials between 0.2 and 0.02 μm in diameter. There was a strong negative correlation between salinity and freezing temperatures, and a strong positive correlation between the fraction of meteoric water in each sample and freezing temperatures, possibly due to INPs associated with terrestrial run-off. Spatial patterns of INPs and salinities in 2014 and 2016 were similar. However the concentrations of INPs were higher on average in 2016 compared to 2014, and INP concentrations were enhanced in the microlayer compared to bulk seawater in several samples collected in 2016. Average concentrations of INPs measured in the Canadian Arctic marine boundary layer fell within the range of INP concentrations measured in other marine boundary layer locations. The ratio of measured mineral dust surface area to sea spray surface area ranged from 0.03 to 0.09. Based on these ratios, and the ice active surface site densities of mineral dust and sea spray aerosol determined in previous laboratory studies, mineral dust is a more important contributor to the INP population than sea spray aerosol for the samples analysed. Based on particle dispersion modelling, the source of INPs in the Canadian Arctic marine boundary layer during the summer of 2014 was from continental regions such as the Hudson Bay area, eastern Greenland, or northwestern continental Canada. Science, Faculty of Chemistry, Department of Graduate
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