Atmospheric aerosols can impact Earth’s climate and the chemistry of the atmosphere through a variety of processes and pathways. For example, atmospheric aerosols affect Earth’s climate directly by scattering or absorbing solar radiation or indirectly by interacting with clouds and impacting their physiochemical properties. Aerosols are unique microenvironments, distinct from the bulk, and therefore their physiochemical properties result in differences between bulk and aerosol phase processes, such as reactivity and kinetics, acidity and interaction with light. Despite the fact that the effects of aerosols on atmospheric chemistry have been studied in previous work, there remains considerable uncertainties associated with aerosol chemistry resulting in gaps between atmospheric chemistry models and field observations. By better understanding chemical processes occurring within aerosols, as well as cloud or fog droplets, and the factors that influence them, we can help reduce some of the uncertainties in atmospheric models. This dissertation investigates sulfur oxidation chemistry in the atmosphere to better understand factors influencing the rate of oxidation and the extent of formation of inorganic sulfate. In particular, we investigated the influence of various atmospherically relevant conditions (presence of organic compounds, ionic strength, etc.) in the oxidation of inorganic S(IV), sulfite/bisulfite, to inorganic S(VI), sulfate/bisulfate, compounds in the presence and absence of transition metals. Most importantly, a new role of transition metal catalyzed formation of organosulfur compounds has been found. Furthermore, in this dissertation, the further development of the Aerosol Optical Tweezer system to study the chemistry within individual aerosols is discussed. Utilizing the Aerosol Optical Tweezer coupled with cavity enhanced Raman spectroscopy it is shown that this method can be used to investigate changes within a droplet, such as: (i) pH changes induced by coalescence with acidic aerosol; (ii) reactions within the droplet, like monitoring oxidation of S(IV) and; (iii) reaction of glyoxal with sulfite to yield organosulfur compounds. The findings presented in this dissertation can improve our understanding of the factors influencing sulfur oxidation chemistry and help to further develop a method to study the chemistry occurring within single aerosols to reduce some of the uncertainty associated with aerosol chemistry to improve atmospheric chemistry models.

As nanoparticle (NP) surfaces are highly reactive, NPs can interact with environmental and biological systems and undergo complicated surface transformation processes, including ligand adsorption, ligand displacement reactions, surface oxidation. These transformations can significantly alter the physiochemical properties of NPs. Although surface transformations have been proposed in previous studies, information on the details of these mechanisms and the impact on NP behavior remains unclear.

In this dissertation, in-situ ATR–FTIR was employed to better understand surface transformation on oxide NPs (i.e. TiO2). Displacement reactions of ascorbic acid, citric acid, and bovine serum albumin by humic acid show three different behaviors ranging from complete displacement, partial displacement, and no displacement, respectively. The detailed chemistry analyzed using two-dimensional correlated spectroscopy indicate the formation of different types of adsorption modes including outer sphere and inner sphere complexation during the reaction. These reactions are important to understand if NPs are to be used for in-situ environmental remediation. For example, we through combined in-situ ATR–FTIR and molecular dynamic simulations studied how fulvic acid (FA) alters the performance of polyvinylpyrrolidone coated magnetite NPs in crude oil clean-up. Additionally, the effects of surface coatings on TiO2 NP reactivity associated with the formation of reactive oxygen species (ROS) was investigated. The results indicate that the generated ROS on TiO2 NPs under light can be completely quenched by BSA but partially by FA.

Another focal point of this dissertation is on surface oxidation of CuS NPs. The details of oxidation were investigated via in-situ ATR–FTIR in oxygen under various relative humidity (RH) and the formation of sulfate on the surface at higher relative humidity was observed. These surface species were confirmed by microscopic methods including high resolution transmission electron microscope and atomic force microscope infrared-spectroscopy. X-ray photoelectron spectroscopy data suggests that CuS NPs show little oxidation under dry conditions (RH < 2%), while surface oxidation occurs stepwise with increasing RH resulting in distinct products.

Overall, these studies presented in this dissertation provide valuable insights into the details of mechanisms associated with surface transformation and impacts on the reactivity and properties of NPs.

Atmospheric aerosols significantly affect the chemical balance of the atmosphere, the Earth’s climate, biogeochemical cycles and human health. Although these effects have been extensively investigated in previous studies, there is still substantial uncertainty associated with the heterogeneous chemical processes involved. In industrialized nations, people spend most of their time indoors. Given the fact that there is a myriad of available indoor surfaces having large surface to volume ratios (S/V), investigation of the heterogeneous reactions between gas and surfaces of indoor relevance is crucial. However, the detailed chemistry of molecular processes involving indoor surfaces remain poorly understood.

In this dissertation study, laboratory studies have been carried out using transmission Fourier transform infrared spectroscopy (FTIR) to help better understand the heterogeneous reactions between atmospheric acidic gases and mineral dust surfaces. Adsorption and desorption processes of nitric acid, formic acid, acetic acid and pyruvic acid, respectively, on silica (SiO2) were found to be reversible, physisorbed processes via hydrogen bonding. However, adsorption of pyruvic acid on alumina (Al2O3) and titanium dioxide (TiO2), respectively, formed adsorbed pyruvate, zymonic acid and other pyruvic acid oligomers. Additionally, the role of adsorbed water was studied systematically. Water can compete for surface adsorption sites as well as assist the dissociation of adsorbed strong acid. Photochemical reactions of adsorbed aqueous- and gas-phase pyruvic acid, respectively, on oxide surfaces formed different compounds, suggesting the complex nature of surface-adsorbed systems needs to be addressed.

An additional focus of this dissertation was to investigate the indoor surface chemistry between gases and model surfaces of indoor relevance. We developed a method to study the adsorption/desorption kinetics of gases of indoor relevance on model surfaces of indoor relevance by combining experimental measurements, kinetics modeling, as well as molecular dynamic (MD) simulations. The detailed chemistry between limonene with indoor model surfaces was studied. The interaction mode between a hydrophilic surface with hydrophobic compounds (i.e., limonene) was studied using a combination of transmission FTIR spectroscopy and molecular dynamic simulations.

Overall, the research described in this dissertation study provides valuable insights into heterogeneous reactions between atmospheric gases and mineral dust as well as indoor surface chemistry.

Surfaces are ubiquitous in indoor and atmospheric environments. In the atmosphere, surfaces are present in the form of aerosols, which can impact climate by scattering or absorbing solar radiation and influencing cloud formation and precipitation processes. Sea spray aerosols are a major biogenic aerosol, whose physiochemical properties and composition are reflective of the marine environment. In indoor environments, surfaces are extremely diverse, ranging from walls to skin to window glass. Due to the higher prevalence of surfaces indoors, developing a molecular level understanding of surface processes is necessary for accurately understanding the role surfaces play in regulating indoor air quality and consequently the health of the occupants.

In this dissertation, the surface properties and composition of window glass and sea spray aerosols are investigated. These surfaces are probed upon their nascent production and subsequent physical and chemical transformations under environmentally relevant conditions. In both environments, indoors and outdoors, due to the messy nature of authentic surfaces, comparisons are made back to simple model systems to provide molecular mimetics that can be used for future studies. Due to the small size scales of surface processes, higher resolution chemical analyses and imaging techniques reveal the chemical and morphological heterogeneities across the sample surface. Overall, these studies provide insights into how high resolution spectromicroscopic techniques can be utilized to elucidate nanoscale heterogeneous evolution of atmospherically and indoor relevant surfaces, and their subsequent reactions with trace gases.

Atmospheric aerosols directly impact the Earth's climate by scattering and absorbing solar radiation and indirectly by altering the microphysical properties of clouds. Aerosols formed over the oceans, termed marine aerosols, consist of secondary marine aerosols (SMA) formed upon the oxidation of gas phase species and of primary sea spray aerosols (SSA) that are directly emitted from the surface of the ocean. The climate relevant properties of primary SSA are determined by their size and chemical composition, both of which are functions of the ocean's biological activity as well as atmospheric heterogeneous reactions with trace gas species and photochemical aging reactions. This dissertation investigates the impacts of each of these processes on the chemical complexity of SSA by conducting fundamental laboratory studies involving spectroscopic probing of various SSA systems ranging from simple, single component model systems to authentic SSA produced using an indoor ocean-atmosphere facility that replicates the chemical and biological complexity of the ocean and SSA. First, we identified the various chemical species found in SSA and linked their size and temporal changes to the biological activity of the ocean. Next, we used our improved understanding of the molecular speciation of SSA to look in-depth at the atmospheric reactions that alter the chemical and physical properties of SSA, including the heterogeneous reaction with gas phase nitric acid and OH radicals, as well as photosensitized reactions with chromophoric species. We found that the chemical complexity of SSA due to the organic and biological components alters their reactivity and introduces alternative pathways beyond those previously acknowledged. Finally, to aid in future experiments of photochemical aging reactions of SSA, we constructed and validated an LED incoherent broadband cavity enhanced absorption spectrometer (LED-IBCEAS) to detect various nitrogen oxides (e.g., NO2 and HONO). The findings presented in this dissertation improve our understanding of the various chemical and biological controls on the climate relevant properties of SSA, and can ultimately be used to improve the performance of regional and global climate models.

With the development of nanoscience and nanotechnology, the biocompatibility of nanomaterials is becoming increasingly important. As one of the most prevalent nanomaterials, metal oxide nanoparticles in particular are receiving growing attention due to their potential negative impacts to the environmental and human health upon exposure. Nanoparticles, once introduced in biological fluids, can adsorb proteins forming protein corona, which can cause protein conformational change and function loss. Although many studies have been focusing on the above effects, details of protein interaction with nanoparticles and consequential structural change on nanoparticle surfaces still remain unclear as these processes can be affected by various factors. Therefore, a systematic study on the impacts of influential factors on the behavior of proteins at the nano-bio interface is strongly desired.

The research in the present dissertation pursues a greater understanding of the effects of various parameters on the protein-nanoparticle surface interactions and protein structural change upon adsorption. Specifically, nanoparticle- and environmental-related factors including nanoparticle surface chemistry, pH, co-adsorption of phosphate, and temperature were explored. Spectroscopic and thermogravimetric analysis of bovine serum albumin (BSA) adsorption on TiO2 and SiO2 nanoparticles as a function of pH highlighted the importance of both pH and nanoparticle surface chemistry on protein behavior at nano-bio interfaces. The study shows that protein interaction is strongest on TiO2 surface. Especially, at acidic pH, BSA is completely denatured on TiO2 and protein surface coverage was a factor of three to ten times higher than on SiO2. Detailed secondary structural analysis of BSA adsorption with and without the presence of phosphate indicates that the co-adsorption of phosphate could prevent surface-induced denaturation at very acidic conditions. Furthermore, the effects of surface adsorption on temperature-dependent conformational change of BSA and fibrinogen (Fib) on TiO2 nanoparticles was investigated. Adsorbed BSA exhibits much less change in its secondary structure with increasing temperature than its solution phase, whereas Fib in dissolved and adsorbed states display very similar trend in their structural change as a function of temperature. Moreover, to complement our understanding of protein adsorption on nanoparticles, hydrogen/deuterium exchange mass spectrometry was carried out as a novel method to investigate the role of specific amino acid residues in protein-surface interaction.

Thus, the research in this dissertation provide important insights into understanding the behavior of proteins at the nano-bio interface, specifically the effects of various influences on protein-surface interaction and protein structure.

Atmospheric aerosols are generated by the millions globally from the bursting of ocean bubbles, the action of wind on dust, burning processes, and many other sources. Aerosol particles have high surface area to volume ratios and typically contain chemicals in significantly greater concentrations compared to the bulk source. From serving as the seeds for clouds to promoting multiphase chemistry and interacting with cells, aerosols have profound impacts on the climate and human health. Among the many properties of aerosols, one of the most important is pH, a measure of the particle’s acidity. Low pH aerosols have detrimental effects on the lungs, and many atmospheric transformations exhibit pH dependence. Although aerosol pH is critically important, it is challenging to measure due to the very small volumes individual aerosols occupy. As a result, prior to the work presented here, the pH of nascent sea spray aerosol (the largest source of aqueous particles globally) was unknown. Here, a novel method for the determination of aerosol pH and its application to the measurement of sea spray aerosol acidity is presented. It is found that, in just two minutes, these aerosols are acidified to pH levels ranging from 2 to 4 depending on particle size. Following this result, several key causes and effects of aerosol pH are discussed. Acidity is shown to impact the extent of acceleration of S(IV) oxidation in aerosols, an important chemical reaction for the fate of sulfur dioxide emissions and air quality. A unique type of buffering to aerosols is presented next, where the titration of the particle results in a decrease in the organic content of the aerosol, instead of a drop in pH, due to partitioning of acids. Following this, the kinetics of nitrate and chloride depletion for single aerosols is shown for the first time. These processes both modulate aerosol pH and change particle hygroscopicity, which is a central parameter for atmospheric cloud formation. Finally, the link between aerosol acidity and surface chemistry is shown by an exploration of the pH-dependent surface propensity of amino acids in aqueous environments. Together, these studies shed light on the drivers of aerosol pH and the kinetics of critical aerosol-phase reactions. Ultimately, this research improves understanding of the complex ocean-climate system and how invisible particles present health challenges for populations globally.