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New tools and paradigms for the analysis of sea spray aerosols by single particle mass spectrometry


Aerosols can influence the chemistry of the atmosphere as well as also impact global climate by directly scattering light and modifying cloud properties. Sea spray aerosols (SSA) are the second most abundant natural aerosol globally and have the potential to strongly influence atmospheric chemistry and scattering of solar radiation in marine regions. In this dissertation, an ATOFMS was utilized to characterize the chemistry of SSA, focusing on describing the mixing state of the population and also distributions of chemical components within particles. Existing paradigms describing SSA via single particle mass spectrometers (SPMS) were expanded upon and SPMS descriptions of SSA with results from offline spectromicroscopy and quantitative ensemble techniques were unifed. This research was facilitated by the development of a new SPMS data analysis toolkit, which enabled both script-based and visual data exploration all within a single programming environment. Utilizing this toolkit, ATOFMS depth profiling studies of supermicron SSA illustrated that much of the variation in SSA mass spectral signatures is likely due to inconsistent desorption of particles with core-shell morphologies, helping to unify online and offline descriptions of the SSA mixing state. In a study of SSA generated from a model seawater solution, the interpretation of single particle ion signatures were informed by complimentary offline microscopy images and quantitative chemical composition measurements. It was deduced that the high calcium signal and total negative ion yield were likely a product of the coordination of calcium to carboxylate in the desorbed and ionized particle. For the first time, depth profiling and size dependence analyses were coupled to isolate likely microbial ion signatures (BioSS) from within the SSA population. These new paradigms were applied to interpret SSA ATOFMS data sets from collaborative studies, where the influence of biologically mediated changes in seawater chemistry on SSA chemistry and climate impacts were explored. Concentrations of BioSS and warm ice nucleating particles were correlated, suggesting microbe-containing SSA may effectively nucleate ice in marine clouds. Finally, ATOFMS and aerosol mass spectrometry descriptions of SSA helped establish a mechanistic framework illustrating how SSA chemical composition is modulated not only by phytoplankton primary production but also by microbial degradation processes.

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