IMMERSION FREEZING OF NON-PROTEINACEOUS BIOLOGICAL AEROSOL PROXIES & ARCTIC AMBIENT PARTICLES
Cory, Kimberly M
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Ice-nucleating particles (INPs) are particulates that initiate atmospheric freezing in the temperature range between 0°C and approximately -40°C. Bioaerosols are organic materials, such as bacteria, plants, fungi, and/or archaea, that are dispersed into the atmosphere, in solid or liquid phase, causing ice to form at temperatures as high as -1°C. These particles play an important role in climate science because they alter microphysical properties of a cloud and chemical composition of cloud particles and precipitation. However, the research done on INPs has overlooked the potential for biological influences. There are many sources from which these bioaerosols can come; for example, the aerosols can come from the ocean through the bubble bursting process, river and lakes, areas plagued with drought and heavy winds, or even within the snow in regions that coincide with low temperatures. This study attempted to close that gap in knowledge by researching the ice nucleating capabilities of cellulose and particles collected in the world’s northern most town. The first study is the laboratory-based study to characterize ice nucleation efficiencies of several different cellulose samples, and whether the ice nucleation efficiency is dependent on the physical size of the particle. For cellulose, the project focused on nine laboratory-generated samples that were used as proxies to generate a solution that allowed no interference from other cellulose samples. The nine samples were grouped into two categories, normally microcrystalline (Microcrystalline Cellulose, Fibrous cellulose, ⍺-cellulose, and Arbo-cellulose) and nanocrystalline (Nanocrystalline cellulose, 2,2,6,6-tetramethylpiperidine-1-oxyl Cellulose Nanofibers short length, 2,2,6,6-tetramethylpiperidine-1-oxyl Cellulose Nanofibers standard length, Carboxymethylation Cellulose Nanofibers gel, Carboxymethylation Cellulose Nanofibers powder). To test ice nucleation efficiency, the experiments were run on a Cryogenic Refrigerator Applied Freezing Test (CRAFT) at the National Institute of Polar Research (NiPR) and at West Texas A&M University (WTAMU). In the cellulose project, the results showed that the microcrystalline cellulose did not have a clear distinct difference in ice nucleation as compared to the nanocrystalline. This indicated that the ice nucleation efficiency was not dependent on the size of the particle, which opposes the previous observation that the microcrystalline cellulose is more active than the nanocrystalline cellulose materials. For the future studies, a wider variety of cellulose samples needs to be tested to further increase the amount of data available for the atmospheric model, such as the Global Forecast System. This may enable researchers to stimulate what will occur within the atmosphere with a known amount of a specific concentration. Another step needed is a comparison study between laboratory generated cellulose samples and naturally collected cellulose samples that are ambient within the atmosphere. The second project focused on samples collected in Ny-Ålesund, Svalbard, to study the ice nucleation efficiency of suspended particles. There was a total of ten nucleopore filters collected over the period of the entire month of March in 2017. The significant findings in the Arctic project was that there was bimodal ice nucleation, which indicates that there are marine biogenic aerosols coming off the marine microlayer, behavior well matched with the previous marine microlayer results. For further research, samples should be collected during other seasons to determine whether these samples are just seasonal or a year-round occurrence. Another study should also focus on what specifically is occurring with the marine biogenic aerosols to determine what is happening between the atmosphere and the ocean. All of these advances would help to further understand what is happening to the atmosphere and how the scientific community could further determine what will occur when the concentrations of specific particulates are known.