Aerosols impact climate directly by scattering and absorbing solar radiation or indirectly by influencing cloud properties and lifetime. Additionally, aerosols represent one of the most abundant surfaces available for heterogeneous reactions. Further, as aerosols react and age in the atmosphere, their interaction with solar radiation and water uptake can change. Sea spray aerosols (SSA) constitute one of the most abundant natural aerosols in the atmosphere. Understanding how oceanic biological processes affect SSA composition and heterogeneous chemistry remains an active area of research. To study SSA heterogeneous reaction processes, fundamental laboratory studies must be able to reproduce the full chemical complexity of SSA. In this dissertation, we discuss a novel approach to studying SSA chemistry in the laboratory. This approach entails inducing phytoplankton blooms in a laboratory microcosm experiment to study the impacts of natural microbial processes on the chemical composition of seawater and SSA. From these studies, the role of heterotrophic bacteria and their associated enzymes on the chemical composition of SSA are revealed. This dissertation investigates the impact of enzymes, active in both the seawater as well as in SSA, on aerosol physicochemical properties, including nitric acid heterogeneous reactivity that is important for global nitrogen cycle. Not only can enzymes affect the physicochemical properties of SSA, but they can transform the chemistry of the atmosphere upon coagulation with pre-existing ambient particles. Further, we discovered the roles of monovalent versus divalent cations in the morphology and heterogeneous reactivity lipopolysaccharide-containing SSA. The results uncover the bacterial produced chemicals, including hydrolytic enzymes and lipopolysaccharides, in controlling SSA composition and heterogeneous reactivity in the atmosphere.

Ice-nucleating particles (INPs) are rare particles in the atmosphere that can have disproportionately large impacts on several climate-relevant properties of clouds, including their contribution to precipitation outcomes and the cooling of the earth’s surface. Ice nucleation occurs on scales that are relatively small compared to model grid cells (down to nanometers), and thus are commonly parameterized for representation in cloud or climate models. However, critical gaps in knowledge challenge the development of ice nucleation representations. Challenges include the up to five order of magnitude span in observations of INPs at any given temperature, the numerable INP sources of varying strengths, and the fact that little is known about which properties make an aerosol an INP. Of the common INP species, desert dust is thought to be the most globally important due to its relative abundance and ice nucleating potential, whereas INPs emitted from the ocean surface are implicated in remote ocean regions far from dust sources. Gaps in INP observations near important dust and marine source regions additionally challenge efforts to advance predictive understanding of INPs. Through a synthesis of observational, laboratory and modelling techniques, this dissertation aims to develop INP instrumentation and methods, identify specific marine ice-nucleating entities, and provide observations of INPs near major dust sources. Key results include an automated instrument for measurement of immersion-mode INPs, best practices for offline INP analysis of precipitation samples, INP observations from a shipborne campaign over the Red Sea, Indian Ocean, Arabian Gulf and Mediterranean, and identities of 14 ice-nucleating microbes, at least 2 of which are high likely marine in origin. Finally, to address challenges that inhibit the implementation of improved INP representation in climate models, a data processing “pipeline” is described that will facilitate hydrometeor phase evaluation of the Department of Energy Exascale Earth Systems Atmosphere Model (EAMv1). In summary, this dissertation addresses challenges to the development and application of improved representations of ice nucleation in climate models from both the observational and modeling perspective.

Aerosols influence climate by directly scatter radiation and affecting cloud properties and lifetime. Biological aerosols (bioaerosols) act as cloud condensation nuclei and ice nucleating particles (INPs) and can impact human and ecosystem health. Oceans, which cover over 70% of the Earth’s surface, comprise an important source of bioaerosols emitted in both primary sea spray aerosol (SSA) particles and formed as secondary organic aerosols (SOA) from biogenic volatile organic compounds (VOCs). However, the influence of marine bioaerosols on clouds and climate remains an area of high uncertainty. In this dissertation, bioaerosols from marine environments were measured in laboratory-based systems and the ambient coastal environment to analyze their impact on cloud formation and on local communities. Studies on the ice nucleating ability of SSA showed supermicron-size SSA particles, rather than submicron, were the predominant source of INPs released from a marine environment. The size of these particles suggests these INPs represented bioaerosols, like marine bacteria, their fragments, or exudates. Bioaerosol emissions in SSA were measured with single-particle fluorescence spectrometry over the course of a mesocosm phytoplankton bloom and showed, for the first time, the fluorescence signature and size distribution of these particles in nascent SSA. To uncover how atmospheric oxidants impact the SSA fluorescence profile, an oxidative flow reactor was used to simulate days of atmospheric aging during a phytoplankton bloom study in an ocean-atmosphere system. This study revealed that aged SSA particles underwent chemical transformations from proteinaceous to humic-like particles, reflected in the loss of protein-like fluorescence and the production of humic-like fluorescence. Applying these online fluorescence methods to aerosols in an urban-coastal environment demonstrated the ability to distinguish and characterize marine and continental air masses. Lastly, we developed a novel system combining a sublimation-condensation flow tube with a matrix-assisted laser desorption ionization matrix and an aerosol time-of-flight mass spectrometer to identify sub-100 nm SOA produced from biogenic VOCs. By improving bioaerosol detection in marine environments and better understanding their ability to seed clouds, the findings from this work enable more accurate representations and parameterizations of marine emissions for global climate models.

The globe is primarily made up of the Earth’s oceans, which contribute biological, chemical, and physical influences towards global environments. However, many of the marine biological impacts, specifically on the chemistry of the atmosphere, are not well understood. Compounds like Dimethylsulfoniopropionate (DMSP), and its derivative Dimethyl Sulfide (DMS), cycle through the marine environment as an exchange of carbon and sulfur among many organisms. DMSP derived DMS is also a major contributor towards irradiation of UV light and nucleation of clouds. Understanding the relationship between DMSP cycling and DMS production allows insight into biological impacts on climate.This thesis addresses how heterotrophic bacteria in the marine environment degrade the organosulfur compound DMSP and produce sulfur containing VOCs. During SeaSCAPE 2019, an induced phytoplankton bloom resulted in an increased production of dissolved DMSP (DMSPd), leading to bacterial transcription of genes coding for the enzyme which cleaves DMSP into the volatile DMS. Following, an increase in dissolved DMS was measured in the wave flume. A mesocosm experiment was conducted to investigate the metabolic pathways and showed novel insights into simultaneous degradation of DMSP into DMS and MeSH by a model organism, the Rhodobacteraceae Phaeobacter sp. La5. From our findings, heterotrophic bacteria influence the formation of DMS through enzymatic cleavage of phytoplankton produced DMSP when bacterial sulfur demand is met with excess sulfur. With these novel findings, continued research on the DMSP cleavage pathway, the genes homologs, their rates of transcription and translation, and enzyme efficiency under varying environmental conditions will better our understanding of how microbes affect the composition of the atmosphere through sulfur cycling.

Aerosols can affect climate and precipitation through their ability to serve as cloud seeds. Of particular interest to this dissertation are the sources of aerosols impacting storms that cross the coast of California. Ice nucleating particles (INPs) are particles capable of triggering heterogeneous ice formation in the atmosphere. Even though they are rare, they can have an outsized effect due to their ability to trigger cloud glaciation even at low concentrations. In this dissertation, the effect of aerosol sources and microphysical properties, particularly those of INPs, upon coastal clouds are studied using a combination of lab experiments, field measurements, remote sensing, and atmospheric modeling. Measurements of ambient particles showed that specific meteorological conditions can lead to the transport of anthropogenic pollution particles to the coast of California from the Central Valley, potentially modifying properties of coastal clouds. The role of meteorological conditions in dictating particle source during a winter storm was also investigated by analyzing precipitation samples and remote sensing of clouds. The features of single particle mass spectrometer measurements of dust and bioparticles are explored and characterized. The findings from these lab experiments are used to develop a novel decision tree for the identification of bioparticles in ambient measurements. For the first time, single particle measurements of marine and coastal INP composition were performed. The major source of INPs active at T = -30 ºC was dust, while sea spray aerosol (SSA) and bioparticles were minor sources. SSA that activated into ice crystals were found to be enriched in organics. A novel methodology was developed to estimate INP sources without using direct measurements of INPs. Bioparticles are found to dominate INPs active at T = -20 ºC. Finally, a series of experiments showed that dust can be resuspended from the ocean and still be able to nucleate ice. Aerosol transport simulations of this phenomenon showed that this process may be important for INP populations in the Southern Ocean.

Aerosol-cloud interactions are one of the largest sources of uncertainty in our understanding of the Earth’s climate system. In order to develop better predictive models and understand how the climate will respond to future changes in atmospheric composition, we must determine the sources and nature of aerosols which serve as cloud condensation nuclei (CCN), thus influencing the properties of clouds. Oceans cover 70% of the Earth’s surface and represent a major source of atmospheric aerosols. Sea spray aerosol (SSA) is formed by the action of breaking waves, whereas secondary marine aerosols (SMA) are formed from the oxidation products of gases emitted from the oceans. Biological activity in seawater (i.e. the life, death, and interactions of marine phytoplankton, bacteria, and viruses) can significantly affect the chemical composition of SSA through processing of dissolved organic matter and SMA through the emission of volatile gases. This dissertation investigates the cloud-relevant properties of SSA and SMA generated using ocean-atmosphere simulators in the laboratory, with a specific emphasis on the influence of biological activity in seawater on the properties of these aerosols. For the first time, SMA was produced from the oxidation of the headspace gases of a phytoplankton bloom grown in natural seawater, enabling measurements of its chemical composition and CCN activity. Overall, these studies show that the formation and properties of SMA are much more sensitive to biological activity in seawater than SSA. In addition, the chemical composition of SMA is highly dependent on the extent of photochemical oxidation, with a distinct shift from organic-rich to sulfate-rich composition in response to increased atmospheric aging. This change in SMA composition leads to a significant change in its hygroscopicity. These results suggest that the properties of SMA evolve temporally in the atmosphere, which has implications for CCN concentrations and cloud properties over the oceans.

Atmospheric aerosols shape Earth’s climate impact human health. Sea spray aerosol is the most abundant atmospheric aerosol by mass. Its composition influences its atmospheric roles and is initially determined by the composition of seawater. Seawater is full of microbial life and can also be heavily impacted by pollution. This dissertation investigates the transfer of bacteria, enzyme activity, and contaminants from seawater to sea spray aerosol. Heterotrophic bacteria significantly shape ocean carbon cycling and the composition of marine organic material by expressing extracellular enzymes. These enzymes transfer to the atmosphere in sea spray aerosol where they can continue to catalyze their chemical reactions. Comparisons of enzyme activities in isolated seawater and sea spray aerosol demonstrate that the enzyme activity of sea spray aerosol is distinct from that of its source waters. Aminopeptidase, lipase, and alkaline phosphatase show similar activity levels in sea spray aerosol despite aminopeptidase being dominant in seawater. This demonstrates that the enzyme activity of sea spray aerosol is tuned to prioritize different reactions in the atmosphere than in seawater. Along with the enzymes they produce, bacteria also transfer to the atmosphere in sea spray aerosol. Our understanding of the airborne microbiome stands to benefit from advances in techniques. Coupling high efficiency aerosol sampling with a high throughput, low biomass 16S gene amplicon sequencing protocol produced a novel workflow for the sampling and sequencing of bacteria in sea spray aerosol. This methodology achieved sequencing success at 4.1 million sea spray aerosol particles and 1046 airborne bacteria. The results demonstrate that different water masses with different bacteria communities produce different sea spray aerosol bacteria communities. Along the many populated coastlines worldwide, pollution significantly impacts seawater composition and has the potential to reach people on land by transferring in sea spray aerosol. To investigate this potential, three dye releases were conducted in coastal waters to mimic coastal water pollution at full scale in the environment. Coordinated aerosol sampling detected the dye in the coastal aerosol up to 668 m inland and 720 m downwind. These findings demonstrate that coastal water pollution transfers to the atmosphere in sea spray aerosol and reaches many people on land through this airborne exposure pathway. Non-targeted high resolution tandem mass spectrometry and 16S gene amplicon sequencing were applied to investigate chemical and bacterial signs of coastal water pollution in coastal aerosol. Chemicals and bacteria identified in a major pollution source were also found in coastal aerosol in onshore winds. The bacteria included members independently linked to sewage pollution and accounted for up to 76% of the bacteria identified in the air. Although more abundant in terrestrial aerosols, the chemicals identified in marine aerosols also indicated pollution in sea spray aerosol.

The oceans cover 71% of the world and are a large contributor of volatile organic compounds (VOCs) and aerosols. Marine VOCs can be produced from marine microbiology and emitted from the atmosphere to undergo oxidative processing to form secondary marine aerosols (SMA). Dimethyl sulfide (DMS) has been studied extensively because of phytoplankton and bacteria’s ability to produce it in large quantities and because of its ability to form sulfate aerosol and contribute to the earths global radiative budget. However, only studying DMS has left many uncertainties on the contribution of marine VOCs on SMA formation. To better understand the impact of marine VOCs, this dissertation utilized phytoplankton bloom experiments to quantify VOC emissions from seawater and oxidation experiments to assess the role of VOCs on the number, size, and composition of secondary marine aerosols. Throughout this dissertation, dimethyl disulfide (DMDS) was found to be produced in larger quantities than expected and play a significant role in impacting aerosol number concentrations. Overall, this dissertation highlights the importance of other VOCs, with and without sulfur, contributing to the overall composition of the atmosphere.

Sea spray aerosols (SSA) are one of the most abundant aerosols in the atmosphere and strongly influence clouds and climate. The impact of SSA on climate is driven by its chemical composition, in particular the composition of organic matter in SSA; however a full understanding of the factors that control the transfer of organic matter from seawater to SSA has remained elusive. Here we use a combination of fluorescence techniques to examine the chemical composition of seawater, the sea surface microlayer, and SSA in order to identify the factors that give rise to the appearance of species in SSA. Moreover, we use state-of-the-art aerosol generation techniques to study the temporal changes in seawater and isolated SSA over the course of phytoplankton bloom mesocosm experiments that mimic rapid changes in ocean biology and chemistry. In this dissertation, a unique SSA fluorescence signature was characterized and the contribution of marine bacteria to SSA fluorescence was explored. Additional experiments discussed in this dissertation examine the timing of transfer for different classes of molecules in seawater, such as protein-like and humic-like substances (HULIS), and factors that control transfer were identified for each molecular class. Further studies on the HULIS produced during phytoplankton blooms reveal the importance of bacterial enzymes on the sea-air transfer of HULIS. This dissertation also examines the reliability of fluorescence to determine HULIS relative concentration in the presence of aggregation processes. Finally, in this dissertation, a novel approach to study the metabolic activity of marine bacteria is presented and the transfer of metabolically active marine bacteria is discussed. The findings presented herein help to unravel the complex chemical and biological factors that control SSA composition in the real atmosphere.

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.