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Abstract

Ice nucleating substances (INSs) can initiate heterogeneous ice nucleation in the atmosphere, affecting ice formation and cloud properties, and impacting the climate and the hydrological cycle. Despite their importance, the identities, properties, concentrations and relative contributions of different INS types in the atmosphere, especially under atmospherically relevant conditions, are still poorly understood. This dissertation aims to improve our understanding of organic and inorganic INSs by studying the effects of coatings on their ice nucleation properties and developing new methods for studying their abundance in the atmosphere. INSs can be transported over long distances and coated with solutes in the atmosphere. Thus, the effects of solutes on the freezing properties of INSs need to be determined to better predict ice nucleation in the atmosphere. While several studies have investigated the effects of solutes on mineral dust INSs, few have studied non-mineral dust INSs. We investigated the effects of the solute (NH₄)₂SO₄, a common atmospheric solute, on a range of atmospherically relevant non-mineral dust INSs and several mineral dusts INSs for comparison. (NH₄)₂SO₄ had little to no effect on ice nucleation by ten non-mineral dust INSs, and enhanced ice nucleation by four mineral dust INSs. These results improve our understanding of ice nucleation by both mineral dust and non-mineral dust INSs under atmospherically relevant conditions. In order to study the properties and contributions of organic and inorganic INSs in the atmosphere, methods are needed that are capable of both quantifying and characterizing INSs. Existing methods have limitations such as low-sample throughput, inaccessibility, and susceptibility to false positives and negatives. We developed a new method using density gradient centrifugation to separate and quantify organic and inorganic INSs. The method was evaluated using several micron-sized inorganic, micron-sized organic, and nanoscale organic INSs. In initial tests, this method was able to effectively isolate and separate micron-sized inorganic and micron-sized organic INSs but was not able to effectively retain nanoscale INSs. A modified method was presented with improved retention of nanoscale INSs. After further characterization and development studies, this method may serve as an accessible technique for studying organic and inorganic INSs.